Iwakuma gave up a career-high seven runs on six hits with two walks in his abbreviated start. The 2013 All-Star has allowed 22 runs in 21 1/3 innings over his last five starts as his ERA has climbed from 2.57 to 3.42 with a 14-8 record.
"My balance in general, upper body and lower body are not linking right now," Iwakuma said through interpreter Antony Suzuki. "I need to make an adjustment. All is never perfect, but I'm usually able to make the adjustment. Not being able to make the adjustment, I'm not able to execute pitches when I need to, and that's what I need to do from here on.
"I want to help the team win, and today I failed."
Iwakuma was perfect through the first 2 2/3 innings and remained deadlocked in a scoreless duel with Angels rookie standout Matt Shoemaker until loading the bases and then losing a tough duel to Albert Pujols in a great at-bat in the third.
Pujols fouled off four 0-2 pitches before looping a double into left field to score three runs. Pujols injured his left hamstring running to second base, hobbling into the bag and then immediately coming out of the game with what later was diagnosed as a cramp.
Pujols is expected to be fine, but it remains to be seen what kind of shape the Mariners are in after a tough loss that seemed to spiral south after his big hit.
"I've seen Albert do that time and time again," Mariners manager Lloyd McClendon said. "That's why he's a future Hall of Famer. I thought that at-bat really wore on Kuma and he never recovered after that. … He made great pitches and a great hitter had a great at-bat."
"It was a tough at-bat," Iwakuma said. "I wanted to be aggressive, attack and get ahead early. And I was able to do that. He kept fighting off everything I threw and got his barrel to the ball and it was just a good piece of hitting. It was a split down in the zone."
Both McClendon and catcher Mike Zunino said Iwakuma was extremely sharp to start the game until he walked No. 9 hitter Efren Navarro and got into trouble, with Pujols applying the big blow.
"That's a mentally draining at-bat," Zunino said. "When that doesn't go your way, you've put everything on the line and just happened to not make one pitch."
Howie Kendrick followed with an RBI double to make it 4-0 in an inning where Iwakuma initially got into trouble by walking two batters. He'd never walked more than two batters in an entire game this season.
The Angels didn't let off the gas as David Freese led off the fourth with a home run and Iwakuma was lifted after a pair of singles sandwiched around his lone out of that frame. Both those runners wound up scoring off reliever Dominic Leone and were charged to Iwakuma, with the seven runs exceeding his previous career-high of six in two different games in 2013.
Iwakuma had been tough on the Angels throughout his three seasons in Seattle, going 5-0 with a 1.64 ERA in eight previous games (seven starts) and Pujols was 3-for-23 (.132) with no RBIs against him until his bases-loaded double.
"We just had really good at-bats," said Angels right fielder Kole Calhoun, who sandwiched a single between the two walks to load the bases. "We got him up in the strike zone and got some good pitches to hit, and Albert has the huge AB with the bases loaded and pulls that ball down the line. That's the breakthrough on that guy. He's kind of been an Angel killer in the past."
With Kansas City rallying for a walk-off win over the White Sox, the Mariners (80-69) find themselves two back of the Royals (82-67) for the final playoff spot with 13 games remaining.
The Mariners woes weren't limited to Iwakuma, as the offense saw its scoreless streak reach 19 innings, dating back to the seventh inning of Saturday's 10-inning loss to the A's, until finally crossing the plate in the eighth inning against Shoemaker.
The 27-year-old right-hander held Seattle to just five hits over 7 2/3 innings to improve to 16-4 with a 3.04 ERA.
"We haven't been good offensively for quite a while," McClendon said. "It's a little bit of a concern. I'm not sure what's going on, but we need to get a big hit somewhere to get us jump-started."
First baseman Logan Morrison went 2-for-3 with a double and scored Seattle's lone run on an infield ground out by Humberto Quintero in the eighth.
"We have to better obviously, but we will," said Morrison. "This is a good one to forget about and come back and get them tomorrow."