The New York Yankees were held scoreless for just the sixth time this season on Thursday, losing 6-0 to Toronto to see their precarious American League East lead cut to just one game.
The Yankees could have gained a two-game advantage over Baltimore with just six games remaining in the regular season but instead suffered their third loss in the last five.
There was better news for New York fans when leading wildcard chasers the Los Angeles Angels fell 9-4 to Seattle to move the Yankees a step closer to securing a post-season berth.
"We know what's at stake right now and we've just got to go out there and keep picking up wins," Yankee Nick Swisher told reporters. "We've got a little six-game playoff race."
Detroit pitcher Doug Fister earlier set an American League record by striking out nine consecutive batters as the Tigers beat the Kansas City Royals 5-4 to boost their playoff hopes.
The win moved Detroit two games ahead of the Chicago White Sox in the American League Central division after the White Sox fell 3-2 to Tampa Bay.
Fister's strikeout streak began with the Royals' final out of the fourth inning and ended with Salvador Perez's ground out to end the seventh.
Four American League pitchers had struck out eight batters in a row. Hall of Famer Nolan Ryan accomplished it twice. Blake Stein, Roger Clemens and Ron Davis each did it once.
Another Hall of Famer, Tom Seaver, holds the Major League record of 10, set in 1970.
"Really it was a simple thing of one pitch at a time," Fister said.
"There was no focus on what happened, where guys were playing or anything else. It was just a matter of, 'Hey let's make this pitch here and make it happen."
Tampa Bay's win moved the Rays to just two games out of a wildcard slot behind Oakland, who lost 9-7 in the American League West to the division-leading Texas Rangers.
The Rangers, whose win was highlighted by pitcher Matt Harrison's 18th victory, now hold a four-game lead over the Athletics with six games to play.
Harrison (18-10) pitched six innings, giving up four runs and seven hits, in becoming the Rangers' first 18-game winner since Kenny Rogers in 2004.
In the National League, the playoff-bound San Francisco Giants have decided not to use suspended slugger Melky Cabrera if he becomes eligible in the postseason.
Cabrera, serving a 50-game ban for a positive test for testosterone, would be available to play if the Giants' postseason went beyond five games.
"It's a decision we had to make early because Melky would have to start rehabbing, and we have decided to develop our roster," Giants manager Bruce Bochy told reporters.
Cabrera, the All-Star Game's most valuable player, was batting .346 with 11 home runs and 60 runs batted in when he was suspended on August 15.
"Our guys have done a good job of stepping up when we needed them to," Bochy said.
"I think it's for the best of this club if you've looked at how they've played and all we've been through. These guys have really done a great job."
The Giants, the 2010 World Series champions, clinched the National League West pennant last week and beat Arizona 7-3 on Thursday.
In the other key National League games, St Louis fell 2-0 to lowly Houston to breathe a little life into the wildcard hopes of the Los Angeles Dodgers.
The Dodgers survived a late rally to defeat San Diego 8-4 and move to three games behind the Cardinals in the wildcard race, still a tough mountain to climb with just six games left.
(Reporting by Ben Everill in Los Angeles, California and Gene Cherry in Raleigh, North Carolina, editing by Nick Mulvenney)