Ethier's first homer in the fifth inning put the Dodgers up 3-1 and his second blast added an insurance run in the eighth for Los Angeles.
The victory went to Ted Lilly (6-9), who struck out seven batters in a five-inning start. He surrendered just one run on four hits and two walks.
Four Dodgers relievers teamed up for three innings of scoreless relief and Javy Guerra racked up his fourth save despite allowing a hit and a walk in the ninth.
Tim Stauffer (5-6) was saddled with the loss despite allowing only two earned runs on three hits in a six-inning effort.
Rob Johnson hit a solo homer to provide San Diego with its only run.