Ianetta's run-scoring single gave the Angels a 2-0 lead in the second inning and his two-run shot in the sixth put LA up 7-2.
C.J. Wilson (11-9) went five innings to collect the win, allowing a pair of runs on five hits. The left-hander walked two and struck out three in claiming his second consecutive start.
A's starter Tommy Milone (11-10) was reached for five runs on 10 hits over just three complete innings.
Chris Carter and Josh Donaldson homered for the American League wild card-leading A's, who saw their nine-game winning streak snapped.