National League East leaders the Washington Nationals suffered a controversial 5-4 Interleague defeat to the Tampa Bay Rays.
The Rays prevailed despite relief pitcher Joel Peralta being ejected in the eighth inning without throwing a pitch after a foreign substance was found on his glove.
But Nationals starter Chien-Ming Wang also suffered, giving up four runs in the third via Carlos Pena's two-run homer and Elliot Johnson's two-run triple.
The win saw Tampa close on divisional rivals Baltimore and the New York Yankees, who were both beaten.
The AL East-leading Yankees saw their 10-game winning streak ended by the Atlanta Braves, Jason Heyward batting in the decisive run in the sixth.
And Baltimore went down 5-0 to the New York Mets, who closed to within three wins of the Nationals in the NL East.
Johan Santana pitched six scoreless innings in a second successive shut-out for his side against the Os and Lucas Duda hit a two-run homer.
The American League West's leading pair, the Texas Rangers and the Los Angeles Angels, both enjoyed comfortable wins.
Josh Hamilton scored two runs as the Rangers downed the San Diego Padres 7-3 while Albert Pujols' three-run homer kick-started the Angels' 12-5 win over the San Francisco Giants.
Divisional rivals the Oakland Athletics claimed a notable scalp with a 3-0 win over National West leaders the Los Angeles Dodgers, Brandon McCarthy allowing just two hits over seven innings having recovered from a shoulder problem.
The Chicago Cubs beat their city rivals the White Sox for the second night in succession, David DeJesus' two-run single earning them a 2-1 success despite Sox pitcher Jake Peavy retiring 16 straight as he pitched the full game.
The Seattle Mariners beat the Arizona Diamondbacks 12-9 after scoring three runs in the first extra inning, Casper Wells hitting a two-run single before being scored by Ichiro Suzuki's second double of the night.
Colby Rasmus and Jose Bautista twice combined for back-to-back homers as the Toronto Blue Jays edged out the Milwaukee Brewers 10-9.
The NL Central leading Pittsburgh Pirates beat American League counterparts the Minnesota Twins 7-2 as Kevin Correia pitched more than five scoreless innings.
The Philadelphia Phillies beat the Colorado Rockies by the same scoreline, while the Miami Marlins were beaten 7-5 by the Boston Red Sox.
The Detroit Tigers beat the St Louis Cardinals 6-3 and the Kansas City Royals beat the Houston Astros 2-0 thanks to 7 2/3 shut-out innings from Luke Hochevar.