Iwakuma gave up five runs (four earned), marking the first time he allowed more than four runs in an appearance. The last time he allowed four earned runs was July 15 against the Rangers.
The 3 2/3 innings pitched by Iwakuma was the first time the 31-year-old rookie from Japan didn't make it through five frames in his 11 Major League starts. He saw his ERA as a starter rise from 2.42 to 2.80 and lost for the first time in five decisions.
"He flattened out that one inning, left some pitches up, over," Wedge said. "Made a couple pitches that he probably shouldn't have, pitch-selection wise. It happened quick."
The A's jumped on the board early, plating a run in the first to break Iwakuma's streak of 10 1/3 consecutive scoreless innings. With two outs and Josh Reddick on first, Yoenis Cespedes hit a grounder down the third-base line. The ball went under third baseman Kyle Seager's glove, allowing Reddick to score from first.
The runs really poured in during the fourth, though, when Iwakuma allowed four runs on five hits. The big blow came from George Kottaras, who sent a rocket into the right-field seats for a two-run shot. The A's catcher has four home runs and 13 RBIs in his past five games.
"Iwakuma has been pitching lights out, so for us to score some runs early off him was pretty impressive after having a good night off of Felix," A's skipper Bob Melvin said.
The poor start by Iwakuma was followed by an excellent outing from rookie reliever Carter Capps. The hard-throwing 22-year-old went a career-high 2 1/3 innings and did not allow a run while striking out four.
"It's great for him to go out there and pitch two-plus innings and have to work through some things," Wedge said. "He's starting to figure it out, he's starting to get a feel for what he needs to do to be successful. It's still very early in his career, of course, but he's getting some good opportunities to go out there and throw 30, 40 pitches; pitch one, two, two-plus innings. That's when you learn something and that's what we're seeing with him. I was very impressed with him today."
Shawn Kelley followed with two scoreless innings, but Stephen Pryor allowed a run in the ninth on a sacrifice fly to snap the Mariners' bullpen scoreless streak at 17 innings.
The lone Mariners run came in the second. Michael Saunders hit a scorching one-out ground-rule double to dead center, moved to third on the next batter after Oakland shortstop Stephen Drew booted a ground ball and scored on a fielder's choice groundout by Trayvon Robinson to tie the game, 1-1.
Seattle had multiple opportunities to add runs against A's starter Brett Anderson and the Oakland bullpen, but finished 0-for-7 with runners in scoring position and left nine on base.
"He was tough on us tonight, and at the same time, we did barrel some balls," shortstop Brendan Ryan said. "You saw what [Coco Crisp] did out there in center. Coco's got a lot of room to run stuff down. It's frustrating to see [Miguel Olivo] hit a ball like that to center and you get nothing for it, and [Seager] early on, in the first, I think. That's just the way it goes."