Despite putting the leadoff runner on base in four innings with three walks and the hit batter, the 31-year-old worked around them to hold the Twins in check.
"Iwakuma did it the hard way," said manager Eric Wedge. "He was just getting by all night long. But we've seen him do that before. He just didn't have the same command of his fastball and he had to rely more on his secondary stuff, but he really went out and competed."
Pitching for the first time at Target Field, the former Japanese standout said he never quite got comfortable.
"I couldn't make an adjustment for the mound tilt, so that's why I struggled with my control," Iwakuma said through interpreter Daisuke Sekiba. "The mound felt different. I was really struggling to get the first hitter, so I tried to fight it by myself. I tried hard to not let them get any runs and come back."
A night after being baffled by Felix Hernandez, the Twins couldn't solve Iwakuma, either, as they have scored just two runs on 10 hits in 18 innings.
"He was effectively wild," second baseman Jamey Carroll said. "He was using a lot of his offspeed stuff and his split more. We just couldn't do anything with it."
Iwakuma is now 5-3 with a 3.40 ERA, and 4-2 with a 2.71 ERA in 10 starts since July 2. His past two wins have come against the Twins, who have yet to score an earned run against him in 13 innings.
Seattle's rotation has combined to go 19-8 with a 2.74 ERA over the last 37 games, a large reason why the club has pulled its way back near the .500 mark.
A little offense goes a long way with that type of pitching, and the Mariners have improved there, as well, recently.
Ackley's fifth-inning blast off Twins rookie Scott Diamond was his 10th of the season. Seattle now has five players with double-digit home runs for the first time since 2009 -- Kyle Seager with 15, Justin Smoak, Jesus Montero and Michael Saunders with 14, and Ackley with 10.
"It was an 0-1 fastball, just middle in a little bit," Ackley said, before Smoak teasingly suggested Diamond's offering was actually right down the pipe.
"Or it might have been right down the middle," Ackley said with a grin. "It had to be for me to get that one out right now. I knew I hit it well, but out of the box I took off [thinking] like double, triple, inside-the-parker, because you never know with the walls out there which way the ball is going to kick. I didn't know if it was out, but I knew I hit it pretty well."
Diamond confirmed Smoak's suspicion.
"He got a fastball. I just left it right in his bat path, middle-middle," Diamond said. "He did what he needed to with it. It wasn't a good pitch. I didn't locate it at all. I've got to be better than that."
Seager went 2-for-4, and his two-run double in the third increased his team RBI lead to 75. Shortstop Brendan Ryan checked in with a 3-for-4 night with a pair of doubles and two runs as he pushed his average back over the Mendoza Line at .202.
Both of Ryan's doubles scooted right down the third-base line, just inches from going foul. But after a tough season, he'll take those every time.
"I hope I don't have to work with that kind of window to get hits," he said, "but it's nice when they do find the chalk or whatever, because they were hugging it."
Iwakuma gave up his unearned run in the third when he walked the first two batters and then saw them move into scoring position on a passed ball when Miguel Olivo had a pitch down the middle go off the heel of his glove.
Ben Revere then connected on a sacrifice fly to center for the Twins' first run in 12 innings this series. Ryan Doumit added an RBI double in the ninth off Charlie Furbush before Tom Wilhelmsen was summoned to record the final out for his 20th save.
Carroll managed Minnesota's only hit against Iwakuma with a one-out single in the fifth. The Twins finished with four hits off five Seattle pitchers, as their record fell to 52-77, the worst mark in the AL.