So the veteran righty stepped up Saturday with a dominant seven-inning outing in a 1-0 win over Houston, allowing just two hits and striking out eight in a game the Mariners needed to keep the Astros in sight in the American League West.
"It was payback time," said Iwakuma, who was 0-4 with a 7.50 ERA in his past five starts against Houston. "They got me pretty good the last couple starts, and just knowing that, we had to change our game plan, [Jesus] Sucre did a good job behind the plate. He called pitches that I didn't have in mind, and it worked out well. So give a lot of credit to Sucre and the team in general for good defense and the big hit."
The big hit was a triple by Leonys Martin, followed by a run-scoring single by Robinson Cano in the sixth to provide the lone run. But Iwakuma did the heavy lifting on Saturday at Safeco, putting together his best start of the season in improving to 10-6 with a 4.01 ERA.
With Hernandez out, Iwakuma has carried the load for the past two months and is 9-2 with a 3.75 ERA over his past 11 starts. Manager Scott Servais shudders to think where the Mariners would be without Iwakuma as he's helped keep them above water at 46-45.
"We wouldn't be in a good spot, there's no doubt," Servais said. "He's been our most consistent guy, very resilient, good competitor. For me, it goes back to his preparation. He's very professional, has a game plan and the ability to go out and execute it and think through it and make adjustments as the game goes on. He's a veteran, a real pro, and we're very fortunate we've got him."
Iwakuma said stepping up in Hernandez's absence is just what is expected.
"That's part of my job," he said through interpreter Antony Suzuki. "I'm the No. 2 guy. With the King out, we just have to stay patient and fill in and step up until he comes back. Once he's back, I know it's going to be a lot easier for us. Until then, we have to do our job, and that's part of our job, and I'm glad I got the win today as well."
Iwakuma didn't overwhelm anyone with a fastball that topped out at 89 mph, but he mixed his pitches extremely well and the Astros got only a pair of doubles in his seven innings before Edwin Diaz and Steve Cishek came on to preserve the win.
"Iwakuma was awesome," Servais said. "He was back and forth, really good command of all his pitches. He elevated late in some counts and really expanded the strike zone against a pretty good team."
None of that came by chance with the ultra-professional Iwakuma.
"The elevation on his fastball was something where we were looking at the numbers, and the analytical guys brought it to my and [pitching coach Mel Stottlemyre Jr.'s] attention this last week that he maybe wasn't expanding as much up and down," Servais said. "And when he does that, the split is much more effective, and he'll get some chases, too, because he's deceptive up in the zone.
"So great job by everybody, getting the information, people working through it and getting it to the player and then him putting it in play. It was a full team effort."
Astros manager A.J. Hinch said it was a different-looking Iwakuma than the pitcher the Astros had seen earlier in the year, when they scored eight runs in 10 innings in two wins against him.
"You never know how guys are coming off the [All-Star] break," Hinch said. "He had his command, he had his control, he threw a ton of strikes. He could really manipulate the ball today. It didn't look like our hitters were very comfortable."
Greg Johns has covered the Mariners since 1997, and for MLB.com since 2011. Follow him on Twitter @GregJohnsMLB and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.