Matt Wieters went 2-for-4 and drove in three runs while batterymate Miguel Gonzalez yielded just two runs over 6 1/3 solid frames to hand Jon Lester his first loss in 21 career starts against Baltimore.
With just 12 regular-season games left, the Orioles (86-64) hold a one-game lead over the A's for the top spot in the American League Wild Card standings and trail the AL East-leading Yankees by just one game.
"It's nice when you come to the ballpark in general and every game means something," said closer Jim Johnson, who set a new club single-season record by notching his 46th save. "You can feel it amongst the guys in the clubhouse and around the crowds we play in. We're even seeing for the first time Baltimore fans in Boston. I've never seen that before. It's pretty cool seeing how things are changing. It's a good time. We're enjoying the ride, but we're not satisfied."
Saturday's key games to watch (all times ET)
A's (Blackley, 5-3) at Yankees (Nova, 12-7), 1:05 p.m. Preview >
Twins (Deduno, 6-4) at Tigers (Fister, 9-9), 4:05 p.m. Preview >
Blue Jays (Morrow, 8-6) at Rays (Moore, 10-11), 7:10 p.m. Preview >
White Sox (Quintana, 6-4) at Angels (Haren, 11-11), 9:05 p.m. Preview >
Rangers (Harrison, 17-9) at Mariners (Beavan, 9-10), 9:10 p.m. Preview >
If the postseason started today ...
This is how the teams would match up: Postseason Bracket »
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 game 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 the 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 the 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
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.