Hisashi Iwakuma is the most understated ace in the game. This season, he has built upon the success he had in the second half of 2012 and been a stabilizing presence in an iffy Mariners rotation.

Share story

The way Hisashi Iwakuma is going, he just might want to pitch with a blister on his middle finger for the rest of his career. He just might want to consider the limitation of his secret weapon. The Mariners just might want to have Hisashi Blister Night at Safeco Field — the first 15,000 fans with mangled hands get free gloves.

That’s all ridiculous, of course, but what a pitcher Iwakuma is, under any conditions. It seems that nothing will stop him from doing his job, and he’s doing that job as well as anyone in baseball right now.

He’s the most understated ace in the game. This season, he has built upon the success he had in the second half of 2012 and been a stabilizing presence in an iffy Mariners rotation. Now, it appears you can count on Felix Hernandez and Iwakuma to give the team a chance to win every time they’re on the mound. And for an organization waiting for several young, elite pitching prospects to develop, the 32-year-old Iwakuma has been a pleasant surprise in the meantime and a player who is making himself indispensable.

He threw another gem Thursday, helping the Mariners beat Detroit 2-0 and avoid a sweep to close a 10-game homestand that flirted with disaster. In a pitching matchup against the more-celebrated Detroit star Justin Verlander, Iwakuma threw six scoreless innings and needed only 70 pitches to do so. It was an efficient performance from a pitcher who must be careful, in order to manage this blister issue.

Iwakuma didn’t get the win, which, unfortunately, is standard for Mariners starters who bust tail only to watch the offense stammer. Still, even though he had to leave the game early out of fear of irritating that blister, Iwakuma stood among the biggest reasons the Mariners left town without suffering one last gut punch on a homestand full of them.

“Iwakuma was fantastic,” Mariners manager Eric Wedge said.

We can add another adjective to that: Iwakuma is legit, too.

He’s no longer just a pitcher that the American League hasn’t figured out. Thursday marked his 20th start over the past season and a half. And in those 20 starts, he has a 2.44 earned-run average in 121-2/3 innings, including a 1.69 ERA in four starts this season.

How good has Iwakuma been since the All-Star break of 2012? He’s 10-4 with a 2.31 ERA during that span, the best numbers in the American League. The second-best pitcher in that time frame? Verlander, who is 10-5 with a 2.61 ERA.

“The thing about it is, he’s doing it under the radar,” Mariners pitching coach Carl Willis said. “So much of the baseball world gets caught up on power and velocity. But if you can command pitches the way he does and provide the unpredictability of changing speeds, you can be just as effective. That’s what Iwakuma does. He’s a diligent worker. And he has come a long way.”

Remember when Iwakuma came to spring training a year ago? He left his native Japan to give Major League Baseball a try, and, at first, he was seemingly throwing batting-practice pitches at hitters. His ERA resembled LeBron James’ scoring average. The Mariners put him in the bullpen to open the year, and he only made five relief appearances during the first two months of last season.

But after he built strength in his arm and learned the nuances of this league, he received his opportunity. Since then, Iwakuma has thrived.

Asked if he has exceeded his own expectations, Iwakuma says through interpreter Antony Suzuki: “Yes, I have. At the same time, I have to continue to run with it. I want to do anything to help the team.”

It’s incredible that Iwakuma has been so sharp while dramatically changing his preparation habits. Between starts, Iwakuma basically plays catch. He does bullpen sessions, but he only throws 30 pitches, and nothing but fastballs. Mariners trainer Rick Griffin is limiting Iwakuma because only rest will help that burdensome blister.

So, when Iwakuma takes the mound for a game, he is trying his off-speed pitches for the first time in five days. He doesn’t even know how his split-finger fastball, his best pitch, will look. Nevertheless, he’s pitching with great command and control.

“It’s very impressive,” Willis says. “It’s impressive that he still has amazing command at the bottom of the (strike) zone. He doesn’t get to work on it between starts!”

Iwakuma deserves more credit than he’s receiving for his consistent excellence, not to mention his persistence. And he’s about to get his due.

“I don’t think he’s an unknown anymore within the league,” Wedge said.

Nope. He can’t be. He has been too good. And his blister is becoming too famous.

Jerry Brewer: 206-464-2277 or jbrewer@seattletimes.com. On Twitter @JerryBrewer.