Los Angeles has lost two out of three, but has dropped just four of its last 15 games.
Ibanez doubled home a run in the opening inning for the first of his three RBI and Kyle Seager delivered a solo homer in the second.
Seattle then broke things open with a four-run fourth that included a homer from Ibanez. Both Ibanez and Kendrys Morales launched solo shots in the seventh to give the Mariners an 8-0 lead.
Joe Saunders (8-8) worked seven shutout innings to get the win, surrendering five hits with five strikeouts. The three Los Angeles runs came off Danny Farquhar in the eighth.
The loss was charged to Jerome Williams (5-5), who lasted 3 1/3 innings while giving up six runs on seven hits.