The Canadian native got rocked for nine runs (eight earned) on seven hits and six walks in 2 2/3 innings, far and away the poorest outing of his brief time in the Majors. Their third straight loss dropped the Mariners to 83-73, two games back of the Royals for the AL's second Wild Card spot with six games remaining.
"Listen, he's been great and that was one of my concerns about him coming back here, being too charged up and probably a little nervous pitching in front of his countrymen," Mariners manager Lloyd McClendon said. "It's a learning experience. He'll get better from it. Tough loss, we'll move on."
Paxton had never allowed more than three earned runs or walked more than four batters in the Majors. But that all changed for the rookie standout from Ladner, British Columbia, as his season ERA jumped from 2.06 to 3.03 and his record fell to 6-4.
"I just didn't have a good feel for it tonight," said the 25-year-old southpaw. "I felt like I was all over the place. And when I was in the strike zone, it was the heart of the plate and they were hitting balls hard."
After missing nearly four months with shoulder problems, Paxton had given Seattle's rotation a big boost since his August return. But the Mariners staff is wobbling down the stretch with rookie Roenis Elias shut down with an elbow issue and veterans Chris Young and Hisashi Iwakuma struggling of late.
In Seattle's last seven games not started by Felix Hernandez, Mariners starters have a 10.36 ERA with 33 runs and 44 hits in 28 2/3 innings.
"They just didn't get the job done," McClendon said after his club gave up its most runs in a game this season. "These guys have been great all year. Our pitching has been our foundation. But they're only human. I can tell you this, they're out there trying. They're doing the best they can. And we'll come back tomorrow and see if we can win a ballgame."
Hernandez and Paxton had been holding the rotation together recently, but Paxton was in trouble from the start Monday as Danny Valencia's bases-loaded triple and a run-scoring single by Steve Tolleson put Seattle in a 4-1 hole in the first.
The triple ended a streak of 142 straight batters without an extra-base hit off the youngster, second only to a 178-batter streak by Royals reliever Wade Davis among all MLB pitchers this year. That was the second-longest streak in Mariners history behind a 157-batter stretch by Jim Beattie in 1982.
The Jays threatened again in the second with a walk and two singles, but right fielder Chris Denorfia threw Jose Bautista out at the plate for the third out to keep the score at 4-1. But that only delayed the inevitable as Paxton got knocked out in the third when three walks, a double and an infield single ended his night.
"It's tough," Paxton said. "I didn't want to come out and have this start that I had tonight, obviously. They're all important games right now and a game like this is tough. I want to be better. I have to put this one behind me and focus on my routine for the next few days and get ready for the next one."
Reliever Brandon Maurer came into a bases-loaded situation with two out and allowed all three inherited runners to score on a wild pitch and an infield single with an error, leaving Paxton with the nine runs on his ledger.
The Blue Jays, all but eliminated from playoff contention, seemed to relish the chance to spoil Seattle's bid as they played loose, made several outstanding diving catches in the outfield and kept pounding away even after Paxton's departure, with three homers off Seattle relievers.
Third baseman Kyle Seager hit his team-leading 25th homer for Seattle in the sixth, Denorfia went into the second deck with a blast in the ninth and Robinson Cano had an RBI double in the first, but that was far from enough to keep the Mariners from dropping to 5-10 since Sept. 7.
"These type of losses, they're bummers because you're out of it right from the start. But you have to move on and get ready for the next one," McClendon said. "My guys know what's at stake. They're not kids in there. We have to get ready for tomorrow."
It doesn't hurt that Hernandez takes the hill for the second game of the series, but the Mariners have to play better all the way around than they did Monday when they didn't field particularly well, went 1-for-8 with runners in scoring position and gave up 16 hits.
"We know where we stand," said Seager. "But you can't win six games in one night or whatever. You go out and play one game. The math is what it is, but you can only control one game at a time."