None more than in Baltimore, where the Yankees and Orioles squared off in the series opener that once again changed the landscape of the American League East and the AL Wild Card.
After blowing a five-run lead going into the eighth inning, the Orioles battled back to to score four runs in the bottom half of the frame on three home runs to take a 10-6 win and move into a tie with the Yankees atop the AL East.
"Nine innings is an exposer of a lot of things -- 162, games it's pretty relentless and heartless," Orioles manager Buck Showalter said. "But I really liked the look in our guys' eyes from the time the game started."
Baltimore has now won six of its last eight games, while New York, in its biggest slump of the season, has lost six of its last eight contests.
"They're playing with a lot of confidence," said Yankees slugger Alex Rodriguez, who watched as Baltimore blasted six homers -- the most in a game by the club since 2007 -- in the victory over New York. "That was pretty impressive there in the eighth."
The Rangers padded their 5 1/2 game lead over the A's in the AL West, beating the Royals, 5-4, in 10 innings. Ian Kinsler led off the extra frame with a triple, before Michael Young hit an RBI single, which proved to be the difference in the game.
Meanwhile, in the National League, the Braves increased their lead to 3 1/2 games over the Cardinals for the first NL Wild Card spot, beating the Rockies in a tight 1-0 game. Tim Hudson tossed seven shutout innings and Juan Francisco raced home on a mishandled throw back to the pitcher in the win.
However, Atlanta couldn't make up any ground on the Nationals, who beat the Cubs, 9-2, to finish off a four-game sweep and hold onto their 7 1/2 game lead in the NL East. The Nats were led by Kurt Suzuki, who finished the game with a home run and three RBIs, while Ryan Zimmerman had two hits and three RBIs on the night.
Today's key games to watch (all times ET)
Cubs (Wood, 4-11) at Pirates (Burnett, 15-5), 7:05 p.m. Preview >
Sitting 1 1/2 games out of the second NL Wild Card spot, the Pirates will send A.J. Burnett to the hill. His last time out against the Cubs, Burnett held them hitless through 7 2/3 innings.
Marlins (Turner, 1-3) at Nationals (Strasburg, 15-6), 7:05 p.m. Preview >
Strasburg will make his second to last start of the season, with the Nats hoping the 24-year-old can help the team increase their 7 1/2 game lead in the NL East over the Braves.
Yankees (Hughes, 13-12) at Orioles (Chen, 12-8), 7:05 p.m. Preview >
The winner will take sole possession of the top spot in the AL East, with Phil Hughes set to take the hill for the Yankees and Wei-Yin Chen ready to go for the O's.
Braves (Maholm, 11-9) at Mets (Niese, 10-8), 7:10 p.m. Preview >
The Braves will try and solidify their playoff standing as the first NL Wild Card team, as they go for their third straight win.
Astros (Harrell, 10-9) at Reds (Bailey, 10-9), 7:10 p.m. Preview >
The Reds will look to pad their 8 1/2 game lead in the NL Central at home against the Astros. Cincinnati owns a Major League-best 36-17 record since the All-Star break.
Rangers (Holland, 10-6) at Rays (Hellickson, 8-10), 7:10 p.m. Preview>
The Rays are fighting for their playoff life, just two back in the AL East and two games out of the second AL Wild Card spot.
Royals (Mendoza, 7-9) at White Sox (Liriano, 5-11), 8:10 p.m. Preview >
The White Sox will look to increase their slim one game lead over the Tigers in the AL Central with Francisco Liriano set to take the hill.
Brewers (Gallardo, 14-8) at Cardinals (Lohse, 14-2), 8:15 p.m. Preview >
An important piece to the Cardinals holding onto the second Wild Card spot in the NL, Kyle Lohse will take the hill for St. Louis, having won his last eight decisions.
Tigers (Scherzer, 15-6) at Angels (Santana, 8-11), 10:05 p.m. Preview >
Needing every win they can get to stay in the playoff picture, the Angels and Tigers will square off in the first of three games in Anaheim.
A's (Griffin, 4-0) at Mariners (Hernandez, 13-6), 10:10 p.m. Preview >
The A's will look to get back on track after losing three straight and stay at the front of the pack in the AL Wild Card.
Dodgers (Beckett, 6-12) at Giants (Lincecum, 8-14), 10:15 p.m. Preview >
Arguably the biggest series of their season, the Dodgers head to San Francisco for a three-game set against the Giants, sitting 4 1/2 back of them in the NL West.
If the postseason started today ...
Wild Card: A's at Orioles OR Yankees
Division Series: Orioles OR Yankees at White Sox | Rangers at Wild Card winner
Wild Card: Cardinals at Braves
Division Series: Reds at Giants | Nationals at Wild Card winner
To calculate a team's magic number, take the number of games it has remaining on the schedule and add one. Then subtract the difference in the loss column between the team and its closest pursuer.
Tie-breaker games will be played to determine the division winner, even if the two tied clubs are assured of participating in the postseason. If a division championship tie-breaker game is necessary, the head-to-head record between the tied clubs will determine home-field advantage. If the head-to-head record is tied, then division record will be the next tie-breaker.
If two clubs are tied for both Wild Card berths, home-field advantage will be determined by the head-to-head record between the tied Clubs. If the head-to-head record is tied, then division record will be the next tie-breaker.
2012 Postseason Schedule
Wild Card playoff games: Oct. 5
Division Series: Oct. 6-12
American League Championship Series: Oct. 13-21
National League 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.