Rangers 9, Athletics 7: Mike Napoli belted a two-run homer to cap a five-run first inning as host Texas outslugged Oakland to inch closer to securing its third consecutive American League West title.

Ian Kinsler launched his major league-leading seventh leadoff homer to start the game and Michael Young added a two-run single in the first inning for the Rangers, who moved four games ahead of the Athletics and reduced their magic number for clinching the division to three.

Napoli capped the first-inning uprising by depositing a fastball from Travis Blackley (5-4) into the first row of seats in right-center field. The blast was the 21st homer for Napoli, who added an RBI single in the third as Texas matched Oakland in scoring over the next three innings.

Matt Harrison (18-10) benefited from the offensive explosion to secure his fourth straight home victory over Oakland. The left-hander allowed four runs on seven hits in 6 1/3 innings. Joe Nathan worked the ninth for his 36th save.

GAME NOTEBOOK: Texas improved to 23-4 when Kinsler leads off a game with a homer. ... The AL West rivals have split their first 16 meetings this season before returning to California for the A's to host Texas in the final series of the regular season. ... Rangers reliever Mike Adams faced five batters and allowed three homers. Prior to the contest, he had permitted one homer in 51 2/3 innings.