Iwakuma (8-4) yielded three runs on seven hits over seven innings, notching his first triumph since June 10, a span of six starts. The right-hander walked on and struck out seven.
Charlie Furbush tossed a scoreless eighth and Tom Wilhelmsen logged his 19th save for the Mariners, who completed a three-game sweep of the Angels.
Ibanez sent home Brad Miller with a fifth-inning double, handing Seattle what would be a decisive 4-1 lead.
Michael Saunders socked a two-run homer for the Mariners.
Joe Blanton (2-12) was tagged for four runs on five hits over four innings for Los Angeles.
The Angels' Mark Trumbo connected for a solo homer.