Cliff Pennington had three hits and drove in a run in support of the Athletics' Guillermo Moscoso (6-6), who went six innings for the win.
Moscoso allowed three runs -- two earned -- on five hits before turning the game over to three relievers, including Andrew Bailey who was touched for a run in the top of the ninth.
Brian Matusz (1-5) took the loss for Baltimore in his first start since June 30. He surrendered six runs on eight hits in 6 2/3 innings.
The Athletics led 4-1 after three innings but Baltimore cut the gap to one run before the seventh when the A's scored another three runs to take control.
Vladimir Guerrero had two hits for Baltimore, both doubles, and finished with one RBI and one run scored.