The American League Cy Young Award candidate gave up a season-high eight runs in a season-low 4 2/3 innings as Toronto handed the Mariners their fourth straight loss, dropping them three games behind Kansas City in the race for the AL's second Wild Card spot with five games to go.
"Real disappointed," a stunned Hernandez said. "As an ace, I let my team down. That was my fault."
But this late-season swoon has been a group effort as the Mariners have lost eight of their last 11 to fall to 83-74. Seattle's pitching, which had pushed the club into contention for its first playoff appearance since 2001, clearly has hit the wall as the team with the AL's best ERA has been outscored, 42-10, in the last four games.
Outside of Hernandez, Seattle's starters had a 10.36 ERA in the previous eight games, and the recent pitching plague caught up with the ace as well in a fifth inning that turned out to be the worst of his career. He gave up seven runs on five hits with three walks in the frame before being removed with two outs.
The seven earned runs were the most Hernandez has allowed in one inning in his 10-year career.
"I don't know," Hernandez said. "My fastball wasn't there, my changeup was OK. I made a couple mistakes. I missed one play [dropping a bunt] that made that inning bigger. And the walks."
"He just seemed to lose his command in the fifth inning for some reason," said Mariners manager Lloyd McClendon.
Hernandez came into the game with a 0.96 ERA in four September starts, and after a first-inning run had retired 11 in a row before the fifth-inning eruption.
Hernandez's record fell to 14-6 and his ERA jumped from 2.07 to 2.34, which now puts him second behind the White Sox Chris Sale (2.20) in the AL. Hernandez is in line for one more start in Sunday's season finale against the Angels, but it remains to be seen if he'll pitch that game if the Mariners are eliminated.
Seattle's entire rotation has turned rocky down the stretch, with the club going 4-10 over the past two weeks. Rookie Roenis Elias was shut down for the rest of the season with a strained elbow, Chris Young was taken out of the rotation this week following a four-homer game, Hisashi Iwakuma has had a run of six tough starts and James Paxton had the worst start of his young career in Monday's 14-4 loss.
"I don't know," Hernandez said. "We're not tired. We work hard to play the whole year. I don't think it's that. We're just making a lot of mistakes, that's all."
Combined with the Royals' 7-1 victory over Cleveland, the setback leaves the Mariners teetering on the brink with two games remaining in Toronto and three back home vs. the Angels. Seattle is 83-74, while Kansas City is 86-71.
"It's definitely frustrating," said center fielder Austin Jackson, a playoff veteran the past three years in Detroit. "We know the situation that we're in. We're going out there trying to win as many games as possible. This is a tough one. We've got to put it behind us and try to come out tomorrow and win."
McClendon took the same tone, which is really the only choice the Mariners have at this point. A tough 11-game road trip seems to have taken the starch out of Seattle's sails, as they've gone 3-6 on the trip and seen their road record fall to 45-34, no longer the best mark in the AL with two games remaining at Rogers Centre.
"It's tough," McClendon said. "We're not playing well right now and a lot of things are going wrong. But we're still alive. So we'll wake up and come out here and try to win a ballgame tomorrow."
Seattle had taken a 2-1 lead on Robinson Cano's two-run single in the third, but that advantage was short-lived once the Blue Jays sent 13 batters to the plate in the fifth.
Dalton Pompey, a 21-year-old rookie outfielder, led off the frame with his first career home run, a memorable second-deck shot to right that tied the game at 2.
"That's what happens when you fall behind," said Hernandez. "When you're behind, you have to throw your fastball. It was up and he put a good swing on it."
Anthony Gose then doubled, went to third when Josh Thole dropped down a bunt that Hernandez couldn't pick up, and scored on a sacrifice fly by Ryan Goins.
From there the wheels came all the way off as Hernandez -- who came in with the lowest WHIP in the AL -- then gave up a single, two walks, a single, a run-scoring fielder's choice and another walk before being replaced with the bases loaded. His final two runs crossed the plate when reliever Dominic Leone hit a batter and gave up a single before getting the third out.
"It was a big game," said Hernandez. "I just tried to go out there and do what I can do, and I didn't."
Edwin Encarnacion added to the Mariners' misery with a two-run blast off reliever Erasmo Ramirez in the sixth.
Knuckleballer R.A. Dickey pitched seven innings of two-run ball on five hits for the Jays, as he improved to 14-12 with a 3.78 ERA.