Sunday’s Mariners-Rays game in Tampa Bay ended in memorable fashion, with Seattle right fielder Mitch Haniger failing to make a sliding catch on Carlos Gomez’s bloop, mishandling the ball while attempting to pick it up, but recovering in time to throw home, where Johnny Field, who had been running on contact from first base, was out by a country mile. Catcher Mike Zunino could have paused to make an omelette between receiving the ball and applying the tag:

The play preserved the Mariners’ 5-4 lead and gave them not just their 41st victory of the season but their 21st in games decided by one run. With the Astros also winning, 8-7 over the Rangers, Seattle and Houston remained tied atop the AL West. If you haven’t been paying attention lately, the Mariners — while missing the suspended Robinson Cano and overcoming a 5.70 ERA/4.77 FIP from Felix Hernandez — have spent every day since June 2 with at least a share of the division lead. They’ve done this despite the fact that the Astros have by far the better run differential — the majors’ best, actually:

AL West Leaders Team W-L WPct Run Dif 1-Run W-L WPct Other W-L WPct Mariners 41-24 .631 20 21-9 .700 20-15 .571 Astros 42-25 .627 127 6-12 .333 36-13 .735

Now there’s something you just don’t see every day: two teams whose run differentials differ by more than 100 but are basically even in the standings. Those one-run games are the reason. The Astros, who would be on a 109-win pace if they had merely gone .500 in such games to this point, actually won a pair of ’em on Saturday and Sunday, but when it comes to such those contests, they’re still tied for the majors’ fourth-lowest winning percentage and fourth-lowest win total in one-run games. The Mariners, on the other hand, have five more one-run wins than any other team and eight more than any other AL team, though they’re merely third in winning percentage:

Records in One-Run Games Tm W -L WPct Yankees 11-3 .786 Braves 10-4 .714 Mariners 21-9 .700 Brewers 15-7 .682 Red Sox 12-6 .667 Rockies 10-5 .667 Angels 12-7 .632 Phillies 10-6 .625 Pirates 11-7 .611 Athletics 11-7 .611 Padres 8-6 .571 Cardinals 10-8 .556 Tigers 12-10 .545 D-backs 11-10 .524 Indians 10-10 .500 Giants 9-9 .500 Blue Jays 7-7 .500 Rangers 7-7 .500 Dodgers 7-9 .438 Nationals 7-10 .412 Royals 8-13 .381 Cubs 6-10 .375 Marlins 5-9 .357 Rays 9-17 .346 Mets 7-14 .333 Astros 6-12 .333 Orioles 5-10 .333 White Sox 6-14 .300 Reds 5-12 .294 Twins 3-13 .188 SOURCE: Baseball-Reference

Records in one-run games have a lot to do with luck and timing, and it’s rare that a team can sustain a Mariners-like pace over the course of a season. Rare, but not unprecedented: in fact, the two highest season winning percentages in one-run games occurred within the past decade. Here are the top-20 such non-strike seasons since 1901:

Best Winning Percentage

in One-Run Games Since 1901 Rk Tm Year W -L WPct 1 Rangers 2016 36-11 .766 2 Orioles 2012 29-9 .763 3 Pirates 1908 33-12 .733 4 Orioles 1970 40-15 .727 5 Pirates 1909 33-13 .717 6T Senators 1913 32-13 .711 6T Indians 1954 32-13 .711 8 Senators 1925 27-11 .711 9 Reds 1961 34-14 .708 10 Reds 1940 41-17 .707 11 Royals 1980 29-12 .707 12 Red Sox 1986 24-10 .706 13 Royals 1977 31-13 .705 14T White Sox 1959 35-15 .700 14T Giants 2003 28-12 .700 16 Cubs 1907 37-16 .698 17T Athletics 1928 30-13 .698 17T Angels 1985 30-13 .698 19T Athletics 2002 32-14 .696 19T Giants 1912 32-14 .696 SOURCE: Baseball-Reference

These Mariners would be tied for 14th in winning percentage in one-run games if the season were to end today. What’s perhaps more interesting is that, while they’re just about 40% into their season, they’re already halfway to the record for one-run wins:

Most One-Run Wins in a Season Since 1901 Rk Tm Year W-L WPct 1 Giants 1978 42-26 .618 2T Reds 1940 41-17 .707 2T Mets 1969 41-23 .641 4T Orioles 1970 40-15 .727 4T Orioles 1974 40-21 .656 6T Reds 1985 39-18 .684 6T Astros 1979 39-27 .591 8T White Sox 1972 38-20 .655 8T Yankees 1943 38-23 .623 8T White Sox 1967 38-26 .594 8T Giants 1982 38-28 .576 8T Royals 1993 38-32 .543 SOURCE: Baseball-Reference

Both of those lists contain teams that won it all (1907 Cubs, 1909 Pirates, 1940 Reds, 1943 Yankees, 1969 Mets, 1970 Orioles) or at least won pennants (1912 Giants, 1954 Indians, 1959 White Sox, 1980 Royals, 1986 Red Sox), but they also contain teams that didn’t even make the playoffs, such as the 1908 Pirates, 1913 Senators, the record-setting 1978 Giants, and so on — a reminder that eking out a few handfuls of narrow victories isn’t entirely skill-based.

Which isn’t to say skill isn’t involved. Bullpen performance has an outsized effect on a team’s record in one-run games, because unlike on offense, where the batting order may not be at its optimal point(s) at the highest-leverage moments of the game, managers have more control on when to deploy their relievers. In 2016, amid the Rangers’ success, FiveThirtyEight’s Rob Arthur showed a significant correlation (r = .28) between bullpen WAR and winning percentage in one-run games. As it turns out, the Mariners currently rank third in the majors in bullpen WAR (3.3) behind the Yankees (4.1) and Brewers (3.6), two of the teams in their neighborhood in one-run winning percentage. Then again, the Astros are tied for fourth (3.1) — and look where that’s gotten them.

Of course, there’s more to bullpen performance than just WAR, and actual runs allowed — and their timing — both matter. Timing matters in every phase of the game, and it’s worth looking at where the AL West co-leaders stand with regards to our win probability-based Clutch scores, which on an individual level measure “how much better or worse a player does in high leverage situations than he would have done in a context neutral environment.” The Clutch measure compares each player to himself — does he hit or pitch better in higher-leverage situations than overall? — and does a good job of describing the past but not of predicting the future.

On offense alone, the Mariners entered Sunday with four of the AL’s top six offensive clutch scores, with Jean Segura third (0.89), Kyle Seager fourth (0.85), Guillermo Heredia fifth (0.84), and Nelson Cruz sixth (0.83); each has added the better part of an extra win when it comes to Win Probability Added, average Leverage Index (pLI), and context-neutral wins (WPA/LI). At the other end of the spectrum, the Astros’ Carlos Correa (-1.10) ranks fourth from the bottom out of 125 players with at least 150 PA, ahead of only Teoscar Hernandez (-1.11), Mike Trout (-1.32 — it’s tough hitting like Mike Trout all the damn time!), and Giancarlo Stanton (-1.40), with Houston teammate Evan Gattis (-0.69) the 12th-lowest.

Here’s the tale of the tape between the Mariners and Astros:

Mariners vs. Astros Category Mariners (AL Rk) Astros (AL Rk) wRC+ 105 (6) 110 (3) Batting Clutch 2.90 (1) -1.29 (7) SP FIP 3.97 (6) 3.28 (1) SP Clutch 1.49 (4) -0.06 (11) RP FIP 3.30 (4) 2.83 (1) RP Clutch 1.08 (3) -2.12 (15)

Of the two teams, the Astros have the slight edge in wRC+, a modest edge in reliever FIP, and a big edge in starter FIP, and yet the Mariners have the better clutch scores on all three fronts — among the AL’s top three in each category, and with an advantage of at least 1.5 wins in each. There’s a whopping nine-win gap between the two teams on this front:

AL Clutch Scores # Team Bat Clutch SP Clutch RP Clutch Total Clutch 1 Mariners 2.9 1.5 1.1 5.5 2 Blue Jays -0.4 0.0 2.5 2.1 3 Tigers 1.6 1.1 -0.8 1.8 4 Red Sox 1.0 -0.4 0.8 1.4 5 Yankees 2.0 -1.2 -0.2 0.7 6 Rangers -0.9 0.9 0.3 0.3 7 Indians -1.9 1.5 0.4 0.0 8 Angels -1.6 1.0 0.5 0.0 9 Athletics -4.3 0.9 3.2 -0.2 10 Orioles -2.8 2.1 0.3 -0.4 11 Twins -2.1 1.5 -0.4 -1.0 12 Royals -2.1 -0.6 -0.3 -2.9 13 White Sox -2.2 0.2 -1.0 -3.0 14 Astros -1.3 -0.1 -2.1 -3.5 15 Rays -4.2 -0.1 -0.2 -4.6

By comparison, the gap between the two teams in our BaseRuns standings is nine games (Astros 44-23, Mariners 35-30) despite their dead-heat actual records; meanwhile, they’re 11 games apart via PythagenPat (Astros 47-20, Mariners 35-30). The last time I checked, however, they don’t determine playoff status via BaseRuns or PythagenPat, and while it’s true that the AL playoff picture already boils down to just six teams (the Yankees, Red Sox, Astros, Indians and Angels being the others — thanks for playing, everybody else!) competing for five spots, it’s also true that the distinction between a division winner and a Wild Card team remains a major one. That the Mariners, despite their holes and flaws (no production at first base, only two above-average starting pitchers, some shaky contributors in the bullpen) are running neck-and-neck with the well-outfitted defending champions — and ahead of the Angels (37-29) — is impressive no matter how they’ve done it. It doesn’t guarantee an end to the longest postseason drought in professional sports, but it certainly hasn’t hurt.