On June 3, after a spurt of five consecutive games with a home run, Los Angeles Dodgers center fielder Joc Pederson was hitting .267/.393/.606 with 17 home runs. He wasn't just the best rookie in the league, he'd been one of the best players in the league through the first two months.

That hot start carried him into the starting lineup in the All-Star Game, but since June 4 he has hit .186/.308/.311 with four home runs and 58 strikeouts in 196 plate appearances. As his struggles to make contact mount, his patience at the plate also has dwindled, as he has drawn just four walks in July to go with one home run.

Chicago Cubs rookie Kris Bryant entered the season as the top-rated and most-hyped prospect in baseball. After his controversial stint in the minors to open the season, he made his debut on April 17 and while he didn't homer until his 21st game, he then started mashing long balls and through June 22 was hitting .282/.384/.485 with 10 home runs. Over his past 15 games, however, he has hit just .138, dragging his season average down to .251.

So who has been the best rookie in the National League?

Matt Duffy.

The unheralded San Francisco Giants infielder began the season as the team's utility infielder but became the starting third baseman when veteran Casey McGehee flunked his opportunity. Entering Wednesday, Duffy is hitting .304/.345/.468, with nine home runs, 16 doubles, four triples and 46 RBIs.

In what has turned into a crowded race with several good candidates, Duffy leads all NL rookies in Wins Above Replacement:

Duffy, Giants: 3.4

Jung Ho Kang, Pittsburgh Pirates: 3.0

Bryant, Cubs: 2.6

Randal Grichuk, St. Louis Cardinals: 2.6

Pederson, Dodgers, 2.4

(Giants teammate Chris Heston has a 1.5 WAR, but his 11-5 record and 3.14 ERA makes him a strong contender as well.)

If you think Duffy's edge in WAR is simply the result of some statistical mumbo-jumbo, think again. His OPS is .813, Pederson's is .816 and Bryant's is .806. Duffy has put up similar offensive numbers while playing in a pitcher's park. Add in his solid defense at third base and he has been the most valuable rookie in the majors. In fact, the guy who hit three home runs last season at Double-A -- and who just three years ago was drafted in the 18th round out of Long Beach State after hitting zero home runs in his college career -- has been hitting third for the defending champs for the past month.

"Definitely not what I expected," Duffy said a few days ago to the San Francisco Examiner's Steve Kroner.

"He uses the whole field," Giants manager Bruce Bochy said. "He's got a good eye at the plate. He's a tough out. ... I didn't think putting him in the 3-hole would put any added pressure on him, and he's handled it very well."

We'll see if Duffy's power proves to be legit. He hit five home runs in June but has just one this month. However, he's hitting .322 in July, good enough for Bochy to keep in the No. 3 spot. So far, he has thrived on inside pitches, so we'll see if pitchers start working the outer half of the plate more:

ESPN Stats & Info

Duffy's surprising production, along with the offensive improvement from middle infielders Brandon Crawford and Joe Panik, is a key reason the Giants are just a half-game behind the Dodgers despite a rotation that has been shaky aside from Madison Bumgarner and Heston. Somewhere in here, credit has to go to Giants hitting coach Hensley Meulens. Certainly, Duffy has gotten stronger. Still, his junior season at Long Beach State he hit .244 with just eight extra-base hits in 201 at-bats. But he had a good eye at the plate and put the ball in play. He had an illness that had sapped some of his strength, but Giants scout Brad Cameron saw some potential.

"He talked about [Duffy's] athleticism, that he could run some, swung the bat pretty good and was versatile," Giants scouting director John Barr told the Sacramento Bee. "And Brad thought that his junior year at Long Beach was not indicative of what he could further become -- he felt like [Duffy] could still have upside to him."

Nonetheless, you don't expect an 18th-round draft pick who didn't hit a home run in college to develop like this. This article points out that Duffy has lowered his hands this year. That's probably made him a little quicker to the ball on those inside pitches. Duffy said he also started using his lower body more to generate power, telling the the Bee's Matt Kawahara, "Before, I would search for power with my shoulders, and if you do that, you get kind of long with your swing and actually lose power. The guy I kind of look at is Buster [Posey], because he's so good at just staying in his legs. It's unbelievable how he can generate not just power but quickness with his legs."

Similar to how the MVP debate often centers around whether it should go to the best player or the best player on a playoff team, there is a less-heated debate on whether future potential should factor into the Rookie of the Year vote. Nobody suggests Duffy is going to have a better career than Bryant. If the numbers among Duffy, Bryant, Pederson and the others end up close, should prospect pedigree factor into the equation? That could be a factor in the end. But so far, Matt Duffy has been the NL's top rookie.