Iwakuma takes the mound opposite Keuchel as the Mariners wrap up a four-game home set against the Astros on Sunday.
After missing all of April with a torn tendon in his right middle finger, Iwakuma (3-0, 1.76 ERA) hasn't wasted any time finding his form. The right-hander has limited opponents to a .189 average, and his 0.59 walks per nine innings ranks as baseball's best mark among pitchers with at least four starts.
"When it comes to pitching, it's location, location, location," manager Lloyd McClendon told MLB's official website. "It has nothing to do with power and everything to do with location and throwing timing off. And he does that very well."
Iwakuma is coming off his third consecutive eight-inning performance, yielding two runs and six hits in Tuesday's 6-2 victory at Texas.
"I'm not very obsessed with going nine innings. I just go out there and do my part, and I feel like I did my part today," he said through a translator. "I'm just focusing day in and day out, staying strong with my routine. I need to make up for that one month that I lost, so that's all I have in mind."
Iwakuma is 3-0 with a 1.95 ERA in his last four matchups against the Astros. He yielded four runs over 6 2/3 innings opposite Keuchel in his season debut May 3, earning the win in a 9-8 victory at Houston.
While Keuchel (5-2, 2.92) surrendered four runs over six-plus innings and took the loss in that game, he's since posted a 1.42 ERA in winning three straight starts. The left-hander came within one out of throwing his second straight shutout Monday, yielding two runs and five hits over 8 2/3 innings in a 5-2 road win over the Los Angeles Angels.
Keuchel was originally slated to pitch Saturday but after throwing a career-high 128 pitches against the Angels, manager Bo Porter decided to give him an extra day off.
Having posted a 2.15 ERA in winning all four of his road starts, Keuchel is looking to become the first Astros pitcher to win his first five road starts in a season since Jose Lima in 1999.
Keuchel also leads the majors with a 67.7 groundball percentage.
"I feel like I was just as good last year, but balls are being hit to guys more," he said.
The Astros (18-32) had been outscored 20-6 during a four-game losing streak before posting their highest run total of the season in Saturday's 9-4 victory.
George Springer homered twice and drove in five runs after missing the previous two games with a hip issue. The highly touted rookie is batting .306 with six homers and 15 RBIs over his last 16 contests.
"That's pretty impressive," Porter said. "To sit out for a couple of days and the first pitch you see, to hit it out of the ballpark the opposite way, that's definitely good to see. Today was a really good team win all the way around."
The Astros are 17-3 when scoring at least five runs compared to 1-29 when they don't.