The playoff field is narrowing and rosters are set to expand in about a week. September baseball is nearly here, and rookies have had three-quarters of the season to make their mark.

The last time we looked at impact rookies was in early July and, while the composition of the list remains static, the order sure hasn’t.

But first, a correction: Rockies closer Manny Corpas is technically not a rookie, because he spent more than 45 days on Colorado’s 25-man roster in 2006. He was erroneously listed as a reliever on the midseason rookie team. When in doubt, do yourself a favor and check ESPN’s sortable rookie stats.

Click the player names below to get up-to-date stats, but keep in mind the listed stats are through games of Aug. 23 to provide a snapshot.

1. Ryan Braun, 3b, 23, Brewers
AVG: .332 OBP: .378 SLG: .643 AB: 319 HR: 24 2B: 17 SB: 10/14
Though he trails nine other rookies in at-bats, Braun has unquestionably done the most with his playing time: He leads all rookies in average and slugging percentage. Though Milwaukee’s pitching has faltered, Braun and Prince Fielder, in his second full season, have kept the Brewers in the NL Central race. Braun’s defense has lived up to scouting reports in his amateur and (short) minor league career—he’s made 20 errors in 80 starts at third.

2. Daisuke Matsuzaka, rhp, 26, Red Sox
W-L: 13-10 ERA: 3.76 IP: 170 H: 153 SO: 172 BB: 63 HR: 18
With the most innings and the most strikeouts, Matsuzaka is clearly the cream of the rookie pitching crop. And while he’s 26, he’s actually younger than Guthrie and just a few months older than Bannister, the next two most effective rookie pitchers.

3. Troy Tulowitzki, ss, 22, Rockies
AVG: .293 OBP: .364 SLG: .463 AB: 464 HR: 17 2B: 22 SB: 6/11
Taking full advantage of Coors Field (he’s batted .255/.328/.366 on the road), Tulo has helped propel the Rockies to the third-highest runs scored total in the NL and to the fringes of the wild card race.

4. Dustin Pedroia, 2b, 24, Red Sox
AVG: .323 OBP: .394 SLG: .445 AB: 384 HR: 6 2B: 27 SB: 5/5
Like Tulowitzki, Pedroia’s overall numbers benefit from playing in a favorable ballpark, but he’s also hit .303/.373/.410 on the road. Very good numbers for a rookie middle infielder who’s settled in as a two-hole hitter for a pennant contender. Here’s an eerily similar player as a career comp.

5. Jeremy Guthrie, rhp, 28, Orioles
W-L: 7-4 ERA: 3.44 IP: 146 2/3 H: 127 SO: 103 BB: 36 HR: 19
Guthrie’s emergence ranks as the second most pleasant surprise for Baltimore, behind only Erik Bedard’s Cy Young-caliber season. He never has thrown more than 161 1/3 innings in a season—and that was in 2004—which may be a factor in Guthrie’s late fade (3.93 ERA in July, 6.64 in August).

6. Hunter Pence, cf, 24, Astros
AVG: .328 OBP: .354 SLG: .561 AB: 326 HR: 12 2B: 26 SB: 8/12
Pence was the top rookie at the All-Star break, but he’s been overshadowed by a combination of Braun’s exploits and a sprained wrist that caused him to miss a month.

7. Brian Bannister, rhp, 26, Royals
W-L: 10-7 ERA: 3.28 IP: 134 1/3 H: 118 SO: 66 BB: 35 HR: 9
One of four Royals rookies here, Bannister has been invaluable as the club’s No. 2 starter behind Gil Meche. He was off to a fast start with the Mets in 2006 before going down with a fluke hamstring injury. Now if Kansas City can get the same kind of return on Kyle Davies, it could be in business.

8. Tim Lincecum, rhp, 23, Giants
W-L: 7-4 ERA: 3.91 IP: 124 1/3 H: 96 SO: 132 BB: 53 HR: 11
The rookie with the best stuff, if not the best results, Lincecum has gone 3-2, 2.92 with 53-21 K-BB in 52 1/3 innings since the break.

9. Hideki Okajima, lhp, 31, Red Sox
W-L: 3-1 ERA: 1.19 IP: 60 2/3 H: 36 SO: 52 BB: 14 HR: 3
Okajima’s continued dominance (0.84 WHIP) has been an unsung part of the Red Sox’ success—as have Boston rookies. Three rank in the top 10 here. Forget Ichiro and Dice-K (well, not really), Japanese relievers like Okajima, Takashi Saito and Akinori Otsuka provide just as much bang for the buck.

10. Chris Young, cf, 23, Diamondbacks
AVG: .237 OBP: .289 SLG: .470 AB: 443 HR: 26 2B: 21 SB: 21/23
One could dwell on the low average and OBP here, but Young, whose Diamondbacks are one of NL’s best teams, has no rivals when it comes to rookie power-speed combos. His 26 homers are tops, and he trails only Reggie Willits for the stolen base lead. With an outside shot at a 30-30 season, Young could become the first rookie ever to accomplish the feat. Bobby Bonds got there in 1969, his first full season, but he wasn’t a rookie.

11. Travis Buck, rf, 23, Athletics
AVG: .288 OBP: .377 SLG: .474 AB: 285 HR: 7 2B: 22 SB: 4/5
Another rookie who’s missed second-half time to injury (strained left hamstring), Buck arguably has been Oakland’s top offensive player.

12. Reggie Willits, lf, 26, Angels
AVG: .295 OBP: .400 SLG: .342 AB: 342 HR: 0 2B: 14 SB: 25/33
Willits’ surprise season continues, though he’s stumbled a bit in the second half (.270/.387/.296) as pitchers get a better read on him. His .400 on-base percentage and rookie-leading 25 stolen bases as the Angels’ leadoff hitter are big reasons why L.A. leads all AL West teams in runs scored.

13. Delmon Young, rf, 21, Devil Rays
AVG: .284 OBP: .314 SLG: .398 AB: 497 HR: 9 2B: 30 SB: 7/10
It’s been a tough year in a lot of ways for Young, but he does lead all rookies in at-bats and doubles. And he filled in capably in center field in the absence of Elijah Dukes and Rocco Baldelli. Looking for signs of improvement? Young has struck out once every 5.6 at-bats in the second half, down from once every 4.8 in the first. Still surprising to see a sub-.400 slugging percentage though.

14. Josh Hamilton, cf, 26, Reds
AVG: .286 OBP: .376 SLG: .563 AB: 245 HR: 17 2B: 13 SB: 3/6
Though Hamilton’s been limited to just 37 at-bats since the All-Star break because of a wrist injury, he’s batted .324/.405/.676 in that span.

15. James Loney, 1b, 23, Dodgers
AVG: .311 OBP: .362 SLG: .474 AB: 209 HR: 6 2B: 10 SB: 0/1
Loney’s ability on offense and defense finally compelled the Dodgers to move Nomar Garciaparra to third base—and they’ve had no regrets.

16. Kevin Cameron, rhp, 27, Padres
W-L: 1-0 ERA: 1.48 IP: 48 2/3 H: 40 SO: 44 BB: 27 HR: 0
From Rule 5 pick to the pennant race, Cameron didn’t allow his first run until May 29 and still hasn’t given up a home run. As an added bonus, he gave the Padres the bullpen depth to trade Scott Linebrink for prospects.

17. Joakim Soria, rhp, 23, Royals
W-L: 1-3 ERA: 2.48 IP: 54 1/3 H: 36 SO: 59 BB: 17 HR: 2
Octavio Dotel’s trade to the Braves meant more high-leverage innings for Soria, who’s handled the closer’s role with aplomb (14 saves). The Rule 5 pick has been stingy with walks and home runs, and has limited opposing batters to a miniscule .187 average.

18. Akinori Iwamura, 3b, 28, Devil Rays
AVG: .286 OBP: .365 SLG: .394 AB: 350 HR: 4 2B: 14 SB: 10/17
Installed as Tampa Bay’s leadoff hitter on June 2, Iwamura’s batting line has fallen steadily ever since. He’s batted .283/.348/.355 since the break.

19. Alex Gordon, 3b, 23, Royals
AVG: .246 OBP: .320 SLG: .405 AB: 427 HR: 11 2B: 27 SB: 13/16
Though his season numbers will be lower than many projected, Gordon has started hitting for power in the second half (.270/.310/.496).

20. Billy Butler, dh, 21, Royals
AVG: .298 OBP: .357 SLG: .440 AB: 218 HR: 5 2B: 14 SB: 0/0
Butler’s big league games by position: DH—50, LF—6, 1B—4. But boy can he hit. He’s batted .312/.385/.442 in regular play since the break.

ALL-ROOKIE TEAM

C—Carlos Ruiz, Phillies (.260/.330/.398, 26 2B, 43 RBIs)
1B—James Loney, Dodgers
2B—Dustin Pedroia, Red Sox
3B—Ryan Braun, Brewers
SS—Troy Tulowitzki, Rockies
LF—Reggie Willits, Angels
CF—Chris Young, Diamondbacks
RF—Travis Buck, Athletics
DH—Hunter Pence, Astros

SP—Daisuke Matsuzaka, Red Sox
SP—Jeremy Guthrie, Orioles
SP—Brian Bannister, Royals
SP—Tim Lincecum, Giants
SP—Kason Gabbard, Rangers (6-1, 3.65 with 45-26 K-BB in 66 2/3 IP)

RP—Hideki Okajima, Red Sox
RP—Ryan Cameron, Padres
RP—Joakim Soria, Royals
RP—Rafael Perez, Indians (1.83 ERA, 47-11 K-BB in 44 1/3 IP)