With a 5-3 win over the Cubs, the Reds became the first team to clinch a playoff berth, lowering their magic number for the National League Central crown to two games.
At 32 games over .500 for the first time since 1999, Cincinnati can clinch the division with a win over the Dodgers on Friday, combined with a Cardinals loss to the Cubs.
However, the Nationals weren't far behind in the clinch party, earning a 4-1 victory over the Dodgers to claim the second spot in this year's postseason. Behind six solid innings from Ross Detwiler, the Nationals will become the first D.C.-based baseball team to play in the postseason since the Senators played in the World Series in 1933. Washington's magic number to clinch the NL East is eight.
"What's the big deal?" Nationals manager Johnson jokingly asked the local media. "That's fun. It's not what I had my eye on, you know. It's a nice step to get here, but every manager that is leading the division, that's the only thing that matters, winning your division."
The American League Central remained status quo as both the Tigers and White Sox dropped their games on Thursday. After the Tigers fell to Oakland in the afternoon, the White Sox had a chance to extend their Central lead to three games. But Chicago blew a three-run cushion against the Royals and eventually lost on Eric Hosmer's walk-off single.
In the AL East, the Yankees grabbed a one-game lead over the Orioles, who were idle. Ichiro Suzuki continued his torrid pace with a home run and three RBIs, while Nick Swisher belted a grand slam to help the Yankees claim a 10-7 win for their fifth straight victory.
"Baseball is a tough game. That's how I feel right now," Ichiro said through an interpreter after the game. "I haven't changed my approach to the game, and that's why I mean it's a tough game: same routine, same approach, but different results."
The Rays kept their playoff hopes alive with a B.J. Upton walk-off homer in the ninth against the Red Sox, which allowed Tampa Bay to stay 5 1/2 games back for the second AL Wild Card spot.
"We've been missing a little bit of the magic this year and it doesn't get much more magical than that moment right there," manager Joe Maddon said. "Like I've been saying, if you believe you can do it, you can. If you believe you cannot, you cannot. So we've done it before. We just did it again tonight. I want to believe that's who we are."
The Brewers leapfrogged the Dodgers in their pursuit of the second NL Wild Card spot with a 9-7 win over the fading Pirates, who are 5 1/2 games back. Trailing by three runs in the eighth inning, the Brewers scored five unanswered runs to earn their fifth straight win. It put the Crew just 2 1/2 games back of the Cardinals, who swept the Astros with a 5-4 win. And the Phillies throttled the Mets, 16-1, to stay at four games back for the second NL Wild Card spot.
Out West, the Rangers worked some of their late-inning magic to pick up a 3-1 win over the Angels, who fell to 4 1/2 back for the second spot in the AL Wild Card race. Adrian Beltre unloaded a two-run home run against Halos closer Ernesto Frieri in the top of the ninth inning that was the difference. Texas' magic number is 10, with Oakland four games behind the Rangers in the division.
In the NL West, the Giants cruised to a 9-2 win over the Rockies, increasing their division lead over the Dodgers to 10 games while trimming their magic number for clinching the division to three.
Friday's key games to watch (all times ET)
Cardinals (Carpenter, 0-0) at Cubs (Volstad, 3-10), 2:20 p.m. Preview >
Chris Carpenter will make his first start of the season at Wrigley Field as the Cardinals try to hold off the Dodgers and Brewers in the NL Wild Card race.
Braves (Hanson, 12-8) at Phillies (Kendrick, 9-11), 7:05 p.m. Preview >
With a magic number of five, the Braves enter the weekend series hoping to clinch a spot in the postseason, as the Phillies look to gain ground in the hunt for a NL Wild Card berth.
Brewers (Marcum, 5-4) at Nationals (Jackson, 9-10), 7:05 p.m. Preview >
Milwaukee has won five straight games and 23 of its past 29 to climb within striking distance of the Cardinals, who are holding onto the final playoff spot in the NL Wild Card race.
Twins (Deduno, 6-4) at Tigers (Porcello, 9-12), 7:05 p.m. Preview >
Two back in the division, the Tigers are in need of a win to stay in the AL Central and AL Wild Card races as Rick Porcello takes the hill.
A's (Parker, 11-8) at Yankees (Sabathia, 13-6), 7:05 p.m. Preview >
The Yankees will look to create more separation between themselves and the Orioles in the AL East, with CC Sabathia looking to bounce back after two rough starts.
Orioles (Gonzalez, 6-4) at Red Sox (Lester, 9-12), 7:10 p.m. Preview >
Coming off a sweep of the Mariners, the Orioles head to Boston ready to continue their winning ways and challenge the Yankees for the top spot in the AL East.
Dodgers (Blanton, 1-4) at Reds (Arroyo, 12-8), 7:10 p.m. Preview >
With their magic number at two, the Reds will look to move a step closer to clinching the National League Central.
Blue Jays (Villanueva, 7-5) at Rays (Shields, 14-9), 7:10 p.m. Preview >
Going just 3-7 in their last 10 games, the Rays hope James Shields can get them a much-needed win to stay in the AL Wild Card race.
Pirates (Locke, 0-1) at Astros (Gonzalez, 2-1), 8:05 p.m. Preview >
The Pirates are carrying slim hopes into their weekend series with the Astros. They trail the Cards by 5 1/2 games for the second NL Wild Card spot.
D-backs (Miley, 15-10) at Rockies (Pomeranz, 1-9), 8:10 p.m. Preview >
Arizona turns to NL Rookie of the Year candidate Wade Miley as it tries to stay in the NL Wild Card race.
White Sox (Peavy, 11-11) at Angels (Santana, 8-12), 10:05 p.m. Preview >
Jake Peavy will look to increase the White Sox two-game lead in the AL Central over the Tigers, as the Angels and Ervin Santana try to make up ground in the AL Wild Card race.
Rangers (Perez, 1-1) at Mariners (Iwakuma, 6-5), 10:10 p.m. Preview >
The Rangers will try to maintain their healthy four-game lead over the A's in the AL West as they send 21-year-old Martin Perez to the mound.
Padres (Kelly, 2-1) at Giants (Vogelsong, 12-9), 10:15 p.m. Preview >
Winning four straight games to start its homestand, San Francisco has a magic number for clinching the division to three.
If the postseason started today ...
Wild Card: Orioles at A's
Division Series: Yankees vs. White Sox | Rangers at Wild Card winner
Wild Card: Cardinals at Braves
Division Series: Reds vs. Giants | Nationals at Wild Card winner
To calculate a team's magic number, take the number of games it has remaining and add one. Then subtract the difference in the number of losses between that team and its closest pursuer.
A tiebreaker games will be played to determine a division winner, even if the tied clubs are assured of participating in the postseason. If a division championship tiebreaker is necessary, the head-to-head record between the clubs will determine home-field advantage. If the head-to-head record is tied, then division record will be the next tiebreaker.
If two clubs are tied for the two Wild Card berths, home-field advantage will be determined by the head-to-head record between the clubs. If the head-to-head record is tied, then division record will be the next tiebreaker.
2012 postseason schedule
Wild Card playoff games: Oct. 5
Division Series: Oct. 6-12
AL Championship Series: Oct. 13-21
NL Championship Series: Oct. 14-22
World Series: Oct. 24-Nov. 1
Quinn Roberts is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.