This week, there were some things you probably know are not about to change. The Red Sox are a unanimous No. 1 again, which isn't a surprise. And the Yankees, Astros and Indians are still all piled up behind them, with the surprise new entry in the top five this week arriving from Oakland after the A's won their weekend series against the Astros. The hottest teams in baseball are all playing in the Junior Circuit. Editor's Picks Way-too-early Red Sox-Indians playoff preview

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But this situation creates one big question: Which clubs in the National League can step up and mount a challenge to this all-American League front five? The hot hitting of teen phenom Ronald Acuna Jr. early in the week helped encourage our voters to bump the Braves up a spot despite their subsequently getting swept by the Rockies in a four-game series. But the Cardinals are mounting a second-half challenge to the Cubs' lead in the NL Central, powered by Matt Carpenter and an outfield restocked by the farm system that has helped them break out to a 21-11 record under interim manager Mike Shildt. With races in all three divisions, and seven different teams within three games of four different playoff slots, the NL's best bids to challenge the AL for dominance are still establishing themselves.

This week, our panel of voters is composed of David Schoenfield, Eric Karabell, Tim Kurkjian, Bradford Doolittle and Sarah Langs.

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Record: 88-37

Week 19 ranking: 1

J.D. Martinez has continued his season-long hot streak through August. Since Aug. 1, Martinez has a 1.288 OPS, the best mark in the AL. His 14 extra-base hits this month trail just Giancarlo Stanton in baseball. And he has excelled with runners on base -- his .500 batting average with men on in August is second-best in baseball. -- Dan McCarthy, ESPN Stats & Information

Record: 75-49

Week 19 ranking: 2

The Astros are in the midst of a very difficult stretch in their schedule, as evidenced by the fact that Wednesday's 12-1 win over Colorado snapped a nine-game home losing streak, and their falling into a tie in the AL West on Saturday before reclaiming a one-game lead on Sunday. It isn't about to get any easier; the Astros have just two homestands left this season, with 13 of their 19 remaining home games coming against AL West teams. -- Jacob Nitzberg, ESPN Stats & Information

Record: 78-46

Week 19 ranking: 3

Luis Severino has not looked the same since the All-Star break. The young phenom was cruising with a 14-2 record and 2.31 ERA over 20 starts before the Midsummer Classic. Since then, in six starts, the right-hander is 2-4 with a 7.26 ERA, the third-worst mark in baseball. Things looked promising in his last start, however, as he worked through five scoreless innings before allowing a pair of runs in the sixth. New York needs its ace to return to form down the stretch. -- McCarthy

Record: 71-52

Week 19 ranking: 4

With Jose Ramirez running neck-and-neck with Mike Trout in WAR and trying to catch up to Mookie Betts, the AL MVP race is definitely heating up. One thing in Ramirez's favor? Nobody's doing a better job of depositing strikes into the cheap seats -- Ramirez's 10.4 home run rate on pitches in the rule-book strike zone leads the major leagues, outpacing even the reliably excellent Trout (10.0 percent). His .415 Isolated Slugging on pitches in the rule-book zone also leads the majors. -- Christina Kahrl, ESPN.com

Record: 74-50

Week 19 ranking: 6

Back on July 10, the A's were 10 games behind the Astros in the AL West. But not even six weeks later, Oakland briefly tied the division lead on Saturday by beating former Cy Young winner Dallas Keuchel before the A's came up short of achieving the sweep and taking sole possession of first place on Sunday. After they won series at home against both the Astros and Mariners last week, the question now is whether they can repeat the feat at the end of the month when they face Seattle and Houston in their parks. -- Kahrl

Record: 71-52

Week 19 ranking: 5

Entering his start Thursday, Jon Lester had been struggling since the All-Star break. He has allowed a 10.32 ERA, 2.07 WHIP, .383 opponent batting average and 1.205 OPS in his first five post-break starts, all of which were worst among pitchers to make at least five starts since the break. Then Lester threw six scoreless innings against the Pirates. The Cubs will need more of that version of Lester to preserve their NL Central lead. -- Nitzberg

Record: 68-55

Week 19 ranking: 8

What else can we say about Ronald Acuna Jr.? The 20-year-old became the youngest player in baseball history to homer in five straight games, has been one of the best players in baseball since the All-Star break and propelled the Braves to tie their season-best, five-game win streak this past week. Oh, and he'll get another crack at Marlins pitching this week, too. -- Evan Wildstein, ESPN Stats & Information

Record: 69-56

Week 19 ranking: 10

Buster Olney cited the D-backs' defense as one of their sources of strength, especially noting their catching trio's contributions. But their major league lead in defensive runs saved also owes much to Nick Ahmed at shortstop, whose 17 DRS is tied for the best mark among NL infielders. Add in that Ahmed has already set career highs in homers, total bases and walks, and he has graduated from defensive specialist to everyday asset. -- Kahrl

Record: 67-58

Week 19 ranking: 7

Mired in a three-team NL West race they were expected to win easily, the Dodgers are seeing a few of their first-half surprises fade in the second half, with Matt Kemp and Enrique Hernandez struggling at the plate since the All-Star break, while Joc Pederson, Max Muncy and Chris Taylor are all posting OBPs below .290. That's contributing to more close games the Dodgers have struggled to win with closer Kenley Jansen out, though there's hope he'll be back this week. -- Kahrl

Record: 68-56

Week 19 ranking: 9

There's been a lot of talk about Max Scherzer and Jacob deGrom for the NL Cy Young Award, but don't sleep on Aaron Nola and his 2.24 ERA and 0.98 WHIP. His ERA is higher than both Scherzer's and deGrom's, but that WHIP is just .02 higher than deGrom's 0.96. His .199 batting average allowed is lower than deGrom's mark of .205 but higher than Scherzer's .182. -- Sarah Langs, ESPN Stats & Information

Record: 68-57

Week 19 ranking: 14

Matt Carpenter has continued his impressive run since turning his season around. He has hit 30 home runs since May 16, the most in the majors in that span, and almost half as many as the Tigers (61) in that same time. His 1.101 OPS in that span is also MLB's best. His 35-game on-base streak came to an end on Saturday; it was the third-longest such streak in the majors this season. He hit .310 with a 1.216 OPS and 17 home runs during that stretch. -- Langs

Record: 71-54

Week 19 ranking: 13

If the past 10 days are any indication, this season's final weeks will provide a wild ride for the Mariners and their fans. A week ago, Seattle was coming off a four-game sweep of the Astros. Since then, Robinson Cano returned from suspension, while Felix Hernandez went to the bullpen for the first time in his career but will now seemingly move back into the rotation following an injury to James Paxton. And they dropped 2 of 3 to the Athletics. The tough stretch continues this week with series against the Astros and Diamondbacks. -- Paul Casella, ESPN Stats & Information

Record: 69-57

Week 19 ranking: 11

The Brewers are in the thick of the playoff hunt, but whether they can claim a spot in the postseason will come down to how well they play against their own division. After going 2-3 against the Cubs and Cardinals this week, the Brewers are just 21-28 against the NL Central this season compared with 48-29 against the rest of MLB. Of the Brewers' final 36 games, 27 are against divisional opponents. -- Nitzberg

Record: 68-56

Week 19 ranking: 15

The Rockies completed a daunting 28-game stretch to begin the second half, in which every game came against a team with a winning record. Colorado went 16-11 over that span to remain in the hunt for both a wild-card spot and perhaps the first division title in franchise history. Nine of the Rockies' next 11 games come against postseason non-contenders, the lone exception being a pivotal three-game set later this week against fellow wild-card hopefuls the Cardinals. -- Casella

Record: 62-63

Week 19 ranking: 12

Juan Soto now has 15 home runs and is just one shy of tying Ken Griffey Jr.'s 16, in 1989, for the fourth-most homers by a teenager in an MLB season. The most were the 24 hit by Tony Conigliaro in 1964, and Soto's teammate Bryce Harper hit 22 in 2012. But Soto's homers likely won't be enough for the Nationals if the bullpen continues to struggle. JT Riddle's home run Saturday was the fifth go-ahead homer the Nationals have allowed in the ninth inning this season, tied with the Tigers and Marlins for the most such home runs allowed this season. -- Langs

Record: 63-61

Week 19 ranking: 18

The Rays have spent the past month testing out their best prospects at the big league level, and some have taken advantage of the opportunity. Shortstop Willy Adames, 22, struggled to adjust to the majors early on but has been red-hot in August. Through July 31, Adames hit just .200, striking out in 35 percent of his plate appearances, but since Aug. 1, he's hitting .327 and has lowered his strikeout rate to 20 percent. -- McCarthy

Record: 63-63

Week 19 ranking: 17

As the Angels continue to await the return of Mike Trout, fellow outfielder Kole Calhoun continues to do his best Trout impression. When Calhoun went on the disabled list on June 1, he had a .145 average and .374 OPS, both of which ranked dead last among 162 qualified hitters. Since returning on June 18, Calhoun is hitting .295 with a .975 OPS, 12th in MLB. The only players with more home runs than Calhoun's 16 during that span are Matt Carpenter and Nolan Arenado. -- Casella

Record: 63-62

Week 19 ranking: 16

After rising to just three games back in the NL wild-card race as recently as July 31, the Pirates' hopes have been fading fast. Injuries to Jordy Mercer and Sean Rodríguez haven't helped matters, and neither has the team's outfield's performance this month. The outfield that posted the fifth-highest first-half OPS will need to show up again for the Bucs to make a push down the stretch. -- Wildstein

Record: 61-64

Week 19 ranking: 19

If we compare Madison Bumgarner before and after he first landed on the DL with an injury last April, our sample size is small, but the differences appear stark. In 103 starts, from 2014 through his last turn before the 2017 DL stint, he had a 2.89 ERA, 1.04 WHIP, .225 batting average and .358 slugging allowed, and a 26.5 percent strikeout rate. In 27 starts since that initial DL stint (including another DL stint this year), he has a 3.24 ERA, 1.20 WHIP, .238 average and .421 slugging allowed, and a 20.7 percent strikeout rate. So each stat has gone in the wrong direction. -- Langs

Record: 59-64

Week 19 ranking: 20

It hasn't been a welcome return to the majors for Ervin Santana, who has an 8.03 ERA in his five starts since making his season debut on July 25. Despite receiving some of the best run support in that span, he has failed to notch his 150th career win. He'll need a strong finish to justify a good contract in the offseason, when he'll be a free agent. -- Wildstein

Record: 56-70

Week 19 ranking: 21

The Rangers' offense kept rolling last week against the D-backs and Angels, as they are now averaging 6.4 runs per game since the All-Star break, the most in the majors during that span. They also lead the majors in slugging percentage and OPS since the break and are tied for the lead in home runs. Alas, Texas also ranks 28th with a 4.93 team ERA during that time. -- Casella

Record: 55-69

Week 19 ranking: 22

Perhaps the Reds should have sold high on Scooter Gennett at the deadline. After leading all second basemen in OPS in the first half, culminating in his first All-Star appearance, Gennett has limped through the second half with a serious power decline and significantly worse luck on balls in play. As a result, the Reds have struggled with one of the worst offenses since the break. -- Wildstein, ESPN Stats & Information

Record: 54-69

Week 19 ranking: 25

A season already likely to be remembered as the year the Mets became the worst team (by final record) to ever start 11-1 or better also now boasts a franchise record. The Mets scored a franchise-record 24 runs on Thursday in Game 1 of the doubleheader against the Phillies -- their first win by 20 or more runs in franchise history -- and scored 40 runs in a two-game span that began Wednesday, also their most ever. In separate games this season, the Mets have scored 24 runs and allowed 25. Elias Sports Bureau research tells us that the last time a team scored 24 or more runs and allowed 24 or more runs in the same season was in 1894, when the Boston Beaneaters, Chicago Colts, Philadelphia Phillies and Pittsburgh Pirates all did so. -- Langs

Record: 55-69

Week 19 ranking: 23

Earlier in the month, Toronto took three out of four games on the road against the Mariners. Unfortunately, they could not sustain that momentum, going 4-10 over their past 14 games. One person who has played well over that stretch is Marcus Stroman. In his past three starts, Stroman has allowed just six earned runs, good for a 3.38 ERA. -- McCarthy

Record: 49-78

Week 19 ranking: 26

The Padres got Wil Myers back from the DL on Monday but had to find a place to put him. With a crowded outfield and Eric Hosmer at first base, Myers got his first start at third base in the majors on Monday (he played one inning there in 2016). And wouldn't you know it, the ball found him, as Myers racked up eight assists, tied for the most by any third baseman in a game this season, and he made no errors. -- Nitzberg

Record: 51-74

Week 19 ranking: 24

In the midst of a disappointing season, DH Victor Martinez announced Wednesday that this will likely be his last season. Martinez turns 40 in December, and he had arguably the best season of his career with the Tigers in 2014, hitting .335 with 32 HR and 103 RBIs, finishing second in the AL MVP voting to Mike Trout. Martinez was a career .315 hitter across five postseason appearances with the Indians, Red Sox and Tigers. -- Nitzberg

Record: 46-77

Week 19 ranking: 28

After one of the worst slumps of his career, Jose Abreu looks like he has snapped back for the stretch run. Over 48 games from May 27 through July 22, Abreu hit .177 and slugged .298 in 199 plate appearances, but in 25 games since, he's slugging .704 and has ripped nine homers. Adding to excitement on Chicago's South Side? The news that hard-throwing phenom Michael Kopech will be called up for his White Sox debut on Tuesday. -- Kahrl

Record: 50-76

Week 19 ranking: 27

The Marlins might have finally bottomed out. They've lost 15 of their past 19 games and have a 9-19 record since the All-Star break. Frustrations seemed to boil over last week when Jose Urena plunked Ronald Acuna Jr. with his first pitch, leading to an ejection and six-game suspension. Miami is on pace for its third 100-loss season in franchise history, a lowlight the Marlins reached previously in both 1998 and 2013. -- Casella

Record: 37-87

Week 19 ranking: 29

One of the biggest surprise turnarounds this month has been the resurgence of Alex Cobb. Through July, Cobb had a 6.08 ERA, second-worst in baseball among pitchers with at least 15 starts. But in four starts this month, Cobb has posted a 1.55 ERA, capped by Saturday's complete-game win over Cleveland. The key has been his split-fingered fastball, as he has held opponents to a .167 average against the pitch in August. Cobb is signed through 2021, so hopefully this is a sign of what's to come. -- McCarthy

Record: 38-86

Week 19 ranking: 30

The Royals got their first look at the other piece of the Mike Moustakas deal this week, as Jorge Lopez made his debut for the team on Wednesday. Lopez started strong but gave up six runs in 4⅔ innings, including a grand slam to Curtis Granderson, which was the 10th grand slam allowed by Royals pitching this season, most in the majors. He'll get more opportunities down the stretch as the Royals evaluate their young pitching. -- Nitzberg