The Mariners needed all they could get from Iwakuma as closer Tom Wilhelmsen left before the game to be with his wife for the birth of their first child and Brandon League and Steve Delabar were unavailable due to trades with the Dodgers and Blue Jays that were announced postgame.
"He was fantastic tonight and we really needed him to step up," said Mariners manager Eric Wedge. "We were obviously really short in the bullpen and for him to go eight strong innings like he did and pitch the way he did against a very good-hitting ballclub, it was just a great performance."
While the Mariners had their own dramas going on with the trades and Wilhelmsen's situation, Iwakuma dealt quietly with his personal situation after making the grueling 14-hour flight to Japan and returning Saturday.
"I didn't think anything about that, I just was thinking about the game today," Iwakuma said through interpreter Daisuke Sekiba. "I just did the same preparation and mostly tried to pitch and beat the Blue Jays. That was my approach."
After surrendering a leadoff home run to Rajai Davis in the first, Iwakuma shut out the Blue Jays for the remainder of his eight-inning stint while allowing just four hits with three walks on 109 pitches.
Iwakuma improved to 2-2 with a 4.10 ERA this season and is now 1-1 with a 3.41 ERA in five starts after working the first three months as a long reliever.
With Wilhelmsen and League out of the closing mix, rookie Lucas Luetge picked up his first career save by getting the final out in the ninth after veteran Josh Kinney struck out two and then missed a chance at his own first save when Wedge took him out after he walked a batter.
Luetge came in to face left-handed pinch-hitter David Cooper, who drilled a ground ball deep into the hole. But shortstop Brendan Ryan fielded the ball and made a leaping throw to nip Cooper at first for the final out.
"It felt good getting the save," Luetge said. "But it felt even better looking back and seeing Ryan making that play. Off the bat, I thought, 'Man, that's a hit. I've got to work on this next guy here.' So I was pretty pumped about it.
"I threw the ball about 6 inches outside and thought he was just going to take it. But he put his bat out there and it found the hole. Luckily we've got a superstar shortstop over there."
Seattle's offense also continued its upward trend as the Mariners have scored four runs or more in all five games during their current win streak, their longest of the season.
The Mariners scored twice in a first inning that included an unusual play where catcher Jesus Montero laced a line drive that caught second-base umpire Tony Randazzo in the left side as he tried to get out of the way.
At the time, Seattle had runners on first and third and Dustin Ackley -- who had led off with a double and moved to third on Michael Saunders' bunt single -- scampered home as the ball dropped to the turf while Randazzo went down immediately.
But because the ball hit the umpire while he was in the infield, it was ruled a dead ball and Ackley was sent back to third while Montero was given a single. Randazzo eventually collected himself and stayed in the game.
Ackley wound up scoring when John Jaso hit a double-play grounder to tie the game and Kyle Seager followed with an RBI single to make it 2-1. It was Seager's team-leading 63rd RBI of the season and Major League-leading 37th with two outs.
Seattle added an unearned run in the second and made it 4-1 in the fifth with doubles by Ryan and Saunders, with Saunders notching his 35th RBI of the year in a 2-for-4 night.
Iwakuma's 13 strikeouts broke the rookie record of 12 held by Freddy Garcia, Randy Johnson and Mark Langston and were the most he's ever had in a game even in his 11 years in Japan.
"On the first hitter, we got the home run," Iwakuma said. "After that, I just calmed down and concentrated on throwing the ball down. And I got the 13 strikeouts. I'm [normally] not interested in getting strikeouts. I'm a ground-ball pitcher. Fortunately I got 13 tonight, so I'm proud of that. And also it's my first win as a starter, so that's a pretty good night."
It was also a very odd night, with Toronto left fielder Travis Snider taken out in the seventh inning as he was traded midgame in a separate deal with the Pirates and then League and Delabar were sent packing afterward.
"We had no clue," Luetge said. "We kind of felt something was going on because the phone was ringing a lot [in the bullpen]. But they didn't tell us anything. We saw Snider coming out of the game and we thought, 'Oh, he just got traded' and we were joking about how it might be for one of us.
"Then it ends up Steve is going to the Blue Jays. ... You know what time of year it is and you expect these kinds of things," Luetge said. "You just try not to think about 'em. If it's you, it's you. If not, you move on. We still have to play tomorrow ... and we're playing against Delabar."