Cahill and Phillies starter Cole Hamels had a nice and easy duel going in a game that breezed by until the Phillies rallied late. Cahill (8-5) won his second straight start after dropping five straight and spoiled Hamels' bid to win his 10th game.
Scott Sizemore's RBI single in the fourth made it 2-1. Cahill and Andrew Bailey held the lead from there. Bailey got four outs to earn his fifth save of the season.
Cahill struck out six and walked three in 7 2-3 innings, and has allowed one run or less 10 times this season.
Hamels lost his second straight start, but extended his streak of not allowing more than two earned runs to six straight outings.
Hamels (9-4) put runners on base in every inning but the second, but the A's failed to bust the game open with one big swing. In the eighth, they had runners on first and third with one out, but Hamels retired the last two batters on grounders to escape the jam.
Hamels allowed eight hits and struck out five in eight innings.
The Phillies nearly bailed him out in the eighth.
Ross Gload hit a one-out, pinch-hit double. There was a visit to the mound to chat with the righty and Michael Martinez came in to pinch run.
The A's faith in Cahill was rewarded for one more at-bat.
He struck out Jimmy Rollins swinging at a 79 mph curveball. Martinez scampered to third on a wild pitch with Placido Polanco batting. Cahill walked Polanco and that was it for the A's starter.
Bailey, a New Jersey native raised a diehard Phillies fan, retired Chase Utley on a grounder to first.
The A's put Bailey back on the mound in the ninth with little pressure after Mark Ellis' RBI single and Coco Crisp's sacrifice fly off Michael Stutes made it 4-1.
Bailey, though, put two runners on before retiring Ryan Howard on a game-ending double play.
The Phillies had only five hits.
The A's entered with an AL-worst 40 homers until Rosales poked one over the right-field wall for his second home run to tie the game at 1 in the third.
Hamels issued a one-out walk to Crisp in the fourth and Hideki Matsui singled, setting up Sizemore's go-ahead single.
Cahill ran into his toughest jam in the second inning and was fortunate the Phillies only scored one run. He walked Howard and Shane Victorino to open the inning, then struck out the next two batters. Carlos Ruiz singled up the middle for a 1-0 lead.
Notes: Phillies RHP Roy Oswalt has a mild bulging disc in his back and likely won't return until August. ... The A's have hit one home run or less in 29 straight games. The team record is 31 straight back in 1978. ... The Phillies snapped an eight-game home winning streak.
