Justin Verlander (2-2) struck out 12 for the Tigers, but Detroit had a four-game winning streak come to an end.
Iwakuma allowed three hits with a walk in six innings, but the game was still scoreless when he left and he did not figure in the decision.
The win went to Carter Capps (1-1), who surrendered two hits in two innings. Tom Wilhelmsen worked a perfect ninth to earn his sixth save.
Verlander struck out the first two batters in the seventh, but then gave up a single to Robert Andino and Kyle Seager's double to left brought in Andino with the first run of the game. A single by Endy Chavez delivered Seager from second.
Verlander gave up nine hits overall while throwing 126 pitches.