Combined with an awakening offense, that was enough to help Seattle to its fourth straight win as the Mariners kept pace in the wide-open American League Wild Card race.
"He certainly knows how to pitch when he doesn't have his best stuff," said manager Lloyd McClendon. "That's how good he is. I think sometimes we take him for granted, but to be a successful pitcher in this game there are going to be times like that where you have to know how to pitch and he knows how to do that."
Iwakuma improved to 10-6 with a 2.86 ERA as he allowed one run on five hits over seven innings, joining Felix Hernandez (12-3) and Chris Young (10-6) as Mariners pitchers with double-digit victories. Those three have the lowest ERA for a starting trio in the American League at 2.64.
Seattle dropped a 1-0 decision in Baltimore in Iwakuma's previous start, losing a game in which the only run came on a leadoff home run. Since then, they've won four in a row at Safeco Field, improving their overall record to 61-54 and their home mark to 30-31.
Catcher Mike Zunino supplied the offensive oomph with a three-run homer for the Mariners, who have outscored their opponents 28-9 in the last four days.
"To be honest, I was fighting tooth and nail," Iwakuma said through translator Antony Suzuki. "I gave up the lead first and that wasn't good, but I was making sure I kept the team in the ballgame and I was very happy for that three-run home run and then the other run."
Iwakuma surrendered one hit in each of the first five frames, but the only one that hurt him was a first-pitch home run to right fielder Dayan Viciedo with two out in the fourth. It was Viciedo's second opposite-field blast in two days and raised his homer total to 16, with three of those coming in five games against Seattle.
But Zunino more than answered with his own opposite-field shot in the fifth, a three-run rip that moved the 23-year-old catcher back into the team lead with 18 homers. Zunino is tied with Cincinnati's Devin Mesoraco for the most homers by a catcher in the Major Leagues this year and is one shy of Seattle's club record set by Miguel Olivo in 2011.
"That's where I really want to drive the ball when I'm feeling good," Zunino said. "That's where it's directed. I was able to get a good fastball on a 2-0 count and barreled it up. When I'm going well, that right field to right-center is a good comfort blanket for me. It takes a while to trust yourself to let that ball travel and get deep, but hopefully I'm on the right path."
The Mariners' offense seems to be on a better path as a whole as Seattle improved to 8-4 over its last 12 games and is averaging 6.1 runs per game in the eight victories.
"Guys are feeling pretty good," said Zunino. "When everyone is piecing together good at-bats and working hard and meshing like we are now, we're trying to score some runs because we know if we score a few, we've got a good chance with our pitching staff and bullpen."
Designated hitter Kendrys Morales made it 4-1 with a sacrifice fly later that inning as Seattle took advantage of a dropped pop fly by third baseman Conor Gillaspie to score two unearned runs in the four-run frame.
Rookie Chris Taylor went 3-for-4 and now has hits in his first 10 starts at shortstop while batting .395 (15-for-38), Robinson Cano upped his hitting streak to 10 games with a seventh-inning single and Logan Morrison extended his own streak to nine games with a 2-for-4 night.
Cano was 1-for-3 with a walk and is hitting .335, tied with Houston's Jose Altuve for the AL lead, while also adding his career-high ninth stolen base.
The Mariners couldn't get much going early against White Sox southpaw Jose Quintana, who hadn't lost in his previous nine starts and allowed just two singles over the first four innings. But a walk by Chris Denorfia, followed by Gillaspie's error set Zunino up for his game-changing blast.
"It's like we're in a funk," said White Sox skipper Robin Ventura. "If anything can go wrong, it's going to go wrong right now. Quintana was pitching great and then a walk, error and homer does him in. It's a combination of us not playing well and they are playing well."
The White Sox had been outscored 63-19 over their last seven games while going 1-6 as they've fallen to 55-62 in the AL Central. The White Sox are 29-10 against the Mariners since 2010, but Seattle leads this season's series, 3-2, with two games remaining this weekend at Safeco.
The Royals won their fifth straight game on Friday to maintain a half-game lead in the race for the final AL Wild Card spot, but the Mariners and Yankees stayed right on their heels by also winning, while Toronto fell 1 1/2 games back.