Dustin Ackley hit his first career grand slam, Michael Saunders homered twice and the Mariners roughed up Cy Young knuckleballer R.A Dickey, beating the struggling Toronto Blue Jays 8-1 on Saturday for their sixth win in seven games.
Iwakuma (3-1) allowed one run and five hits in seven innings. He walked three and struck out five, lowering his ERA to 1.61.
"He has been so consistent for us this year and again he was today," Mariners manager Eric Wedge said.
Since he joined the rotation last July, Iwakuma has gone 11-5 with a 2.32 ERA in 23 starts. He said he's learned a lot about watching Hernandez work ahead of him, and has been trying to imitate his Cy Young winning teammate.
"Seeing him pitch the day before I pitch, you kind of analyze that and take advantage of that," Iwakuma said through a translator.
Seattle's offensive outburst was welcome news for Iwakuma, who'd received just one run of support in his previous three outings.
"Kuma has been pitching about as good as you can ask a starting pitcher up here to pitch," Wedge said.
Yoervis Medina pitched the eighth and Oliver Perez worked the ninth for the Mariners, who have won seven of their past eight meetings with Toronto.
Blanked by Hernandez and reliever Tom Wilhelmsen on Friday, the Blue Jays struggled to get anything going against Iwakuma, finally snapping a 23-inning scoreless streak on Munenori Kawasaki's sacrifice fly in the seventh.
Toronto loaded the bases in the first thanks to a pop-up that Ackley lost in the sun, but Colby Rasmus struck out on three pitches and Rajai Davis fanned to end the threat.
"I was as impressed as anything with that first inning," Wedge said. "You talk about big league pitching, that's big league pitching right there. To get out of that the way he did, especially early in the game, it helps to not necessarily set the tone, but push your squad in the right direction early."
Saunders homered on Dickey's second pitch of the game, the second leadoff homer of his career, and then added another solo shot in the fifth. It was the fourth multihomer game of his career and his first this season.
Saunders added an RBI double off Brett Cecil in the ninth and finished 3 for 5 with three RBIs.
"He had a big day for us," Wedge said. "He just brings a lot of energy and intensity to the top of our lineup."
Ackley connected on a 3-2 pitch in the fourth, immediately after Dickey (2-5) had loaded the bases with back-to-back walks.
"That's an awesome feeling," Ackley said. "Hitting a home run in general is a great feeling, but to have three guys on base and to put your team up, it was pretty important for us."
The blast to center was Ackley's first homer of the season, and Dickey's biggest regret of the afternoon.
"Outside of that I wasn't too disappointed, but that singular pitch really put us in the hole, big time," Dickey said.
Toronto has lost four straight and has been outscored 25-3 since Tuesday's 9-7 comeback win over Boston. A season-worst 11 games below .500, the Blue Jays have lost 14 of 18 overall.
"We're somewhat of a dysfunctional team right now," Dickey said. "We're kind of searching for a way to score runs, a way to pitch well. We're doing a lot of things poorly, myself included."
Dickey (2-5) was booed by the crowd of 35,754 after Raul Ibanez hit a one-out triple to center in the sixth and scored on Kelly Shoppach's double. As the runs piled up, some fans responded with chants of "Go Leafs Go" for the NHL's Maple Leafs, currently in the playoffs against the Boston Bruins.
"I did hear them, it was hard not to," Dickey said. "They were pretty animated. You can't blame them. We've played well below our expectation. We're booing ourselves. It's tough."
Pitching on an extra day of rest because of lingering neck and back soreness, Dickey lost his third straight start. He allowed six hits, including a season-high three home runs. He walked two and struck out five.
Dickey said his neck and back weren't a concern against the Mariners, and manager John Gibbons said the Blue Jays see no need to put Dickey on the disabled list.
Dickey lost consecutive starts only once during his NL Cy Young season with the New York Mets in 2012. His last three-start losing streak came in July and August of 2011.
It was a bad day all around for the Blue Jays, who even appeared to lose track of the number of outs and were slow to come off the field after Kendrys Morales struck out to end the fifth.
NOTES: Wedge gave 1B Justin Smoak and OF Jason Bay the day off against Dickey. ... Dickey underwent an MRI on Wednesday that revealed mild inflammation in his neck and back. It's the same injury that forced him to leave after the sixth inning of an April 18 start against the Chicago White Sox. ... Dickey went 5-8 with a 5.21 ERA in 32 games for Seattle in 2008. ... Seattle's Joe Saunders (2-3) faces Brandon Morrow (0-2) in Sunday's series finale.