David Price's 18th win took him to the top of the American League standings and ensured the Tampa Bay Rays beat the New York Yankees 6-4.
The Rays were four games behind the East League's joint leaders the Yankees and the Baltimore Orioles before the latest round but Price got the better of New York pitcher CC Sabathia.
And Tampa were further boosted after the Orioles also fell to defeat against the Oakland Athletics.
Yoenis Cespedes, batting with a sore wrist, plundered a two-run homer in the fourth inning to help the Athletics to a narrow 3-2 success.
Chicago maintained their one-game lead over the Detroit Tigers in the Central League following a 6-0 drenching of the Minnesota Twins, with Dayan Viciedo hitting two RBIs and Kevin Youkilis a solo homer.
League rivals the Tigers ensured they kept pace and were equally impressive in their comprehensive 4-0 thumping of the Cleveland Indians.
Josh Hamilton's homer propelled West League leaders the Texas Rangers to a 9-3 win over the Seattle Mariners, with Yu Darvish also going past 200 strikeouts in his rookie season.
The Boston Red Sox ended a six-game losing streak against the Toronto Blue Jays with an 8-5 victory and Kendrys Morales' two-run homer was pivotal as the Los Angeles Angels beat the Kansas City Royals 9-7.
Andrelton Simmons was the hero as Atlanta edged out National League East leaders the Washington Nationals 2-1.
Simmons scored the winning run in the ninth inning following a throwing error to allow the Braves to squeak home.
The Central League-leading Cincinnati Reds, received a rude awakening after being humbled 4-0 by the Miami Marlins.
The Pittsburgh Pirates lost their seventh consecutive match as Chicago eased to a 7-4 victory, Starlin Castro driving in four runs for the Cubs, which included a three-run homer.
John Mayberry and Ryan Howard struck three RBIs apiece ensured the Philadelphia Phillies sauntered to a 12-6 victory over the Houston Astros.
Jimmy Rollins' lead-off homer set the tone for the triumph while Domonic Brown also had a two-run shot.
Lucas Duda homered and doubled as the New York Mets claimed their first win in seven with a 7-3 win over the Milwaukee Brewers and the Los Angeles Dodgers beat the St Louis Cardinals 8-5.
Consecutive two-run doubles in the first inning from rookies Wilin Rosario and Jordan Pacheco helped the Colorado Rockies see off the San Diego Padres 7-4 and Hunter Pence hit a grand slam as the San Francisco Giants to a 6-2 success over the Arizona Diamondbacks.