The results were mixed.
Daniel Norris turned in a decent performance in his first big-league start but the Mariners fought back for a 7-5 victory to avoid a four-game sweep and keep their slim playoff hopes alive.
Gibbons rested regulars like Jose Reyes, Dioner Navarro and Jose Bautista and inserted several late-season callups into the lineup. Dalton Pompey of Mississauga, Ont., was the leadoff man while the bottom half of the order featured Toronto native George Kottaras, Kevin Pillar, Anthony Gose and Ryan Goins.
Pompey had a decent game with a run, a hit and two walks while Norris gave up one hit and two earned runs over 3 1/3 innings.
"That's a big thing, a lot of guys don't get that chance to come up at the end of the season," Gibbons said. "When (players) go into a new season and they get called up for the first time, it can be a little intimidating.
"(Playing now) is going to help them all, regardless of the results."
Logan Morrison belted a three-run shot for Seattle (84-75) and added a solo homer as the Mariners ended a five-game losing skid. Seattle entered play three games behind the Kansas City Royals and Oakland Athletics in the race for the two American League wild-card spots.
"We're still in the ring, still fighting," said Seattle manager Lloyd McClendon.
Fernando Rodney gave up a solo homer to Kevin Pillar in the ninth inning before picking up his major league-leading 47th save.
Norris retired the first eight batters he faced. On a limit of about 60 pitches, he was pulled after giving up a one-out walk to Kendrys Morales in the fourth inning.
The 21-year-old left-hander, who made four relief appearances earlier this month, excelled in the minor leagues this year but has noticed a dip in his fastball speed since being called up.
"It's obvious my stuff is not really there," he said. "It's tough to try to pitch without your stuff but sometimes that's the competitor (in you) that has to come out.
"I think that's what I tried to do today, was go out there and compete without your big guns."
Todd Redmond relieved Norris and gave up an RBI single to Kyle Seager that cut Toronto's lead to 2-1. Morrison followed with a no-doubt blast to right-centre field that brought three more runs across.
Pompey showed some flashes of his potential throughout the game. He walked in the fifth inning, took second on an errant pickoff attempt, stole third and scored on an Edwin Encarnacion sacrifice fly.
Adam Lind drove in Munenori Kawasaki later in the frame to tie it before Seattle went ahead to stay in the sixth. Morrison took an Aaron Loup (4-4) pitch over the wall for his 11th homer of the year.
"I don't have any idea how I hit that guy. He's filthy," Morrison said. "I blacked out. I don't know what happened. Obviously playing every day has helped my timing. I know this is the type of player I can be."
Mike Zunino added an insurance run by going deep off Dustin McGowan for his 22nd homer of the year. Reliever Yoervis Medina (5-3) worked an inning of relief for the win.
Seattle used nine pitchers while Toronto used six. The Mariners had three errors but outhit the Blue Jays 10-5.
Notes: Announced attendance was 17,173 and the game took three hours two minutes to play. ... It was Morrison's second career multi-homer game. ... The Blue Jays will wrap up their regular season with a weekend series against the Baltimore Orioles. Drew Hutchison (10-13, 4.51 ERA) will start on Friday night against Baltimore's Chris Tillman (13-5, 3.26).
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