Vladimir Guerrero Jr. helped ruin another game at Yankee Stadium, as his two-run homer spoiled what had been a strong start from Clarke Schmidt.

The sixth-inning blast sparked Toronto’s 5-1 win over the Yankees on Sunday, as the Yankees dropped their first series of the young season, with their undermanned offense dominated by right-hander Kevin Gausman over seven scoreless innings.

Schmidt retired the first 13 batters he faced and struck out a career-high eight before he faltered in the sixth.

He was hurt by Anthony Volpe’s first career error, as Volpe couldn’t come up with a George Springer grounder to shortstop with one out in the inning.

Bo Bichette followed with a hard grounder up the middle that a diving Gleyber Torres stopped and turned into a forceout.

But Guerrero made the Yankees pay.

After starting the series by saying he’d never play with the Yankees because of “personal” reasons, Guerrero put another imprint on the series when he followed Bichette’s groundout with a rocket home run to left to give Toronto a 2-0 lead and then took his time circling the bases.

With Michael King warming in the bullpen, Schmidt faced lefty-swinging Daulton Varsho, who hit one into the second deck in right field to make it 3-0 and end Schmidt’s day after three unearned runs.

Schmidt entered with a 8.79 ERA after four miserable starts in which he hasn’t lasted more than four innings, but he was perfect through the first 4 ⅓ innings on Sunday before Matt Chapman doubled down the first base line with one out in the top of the fifth.

Whit Merrifield followed with a two-out walk before Schmidt got a visit from pitching coach Matt Blake.

Schmidt then got Danny Jansen to fly to center to end the game’s first scoring threat.

The Yankee lineup was no match for Gausman, who struck out 11 and they avoided their first shutout of the season only because of Anthony Rizzo’s homer with two outs in the bottom of the ninth.

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Gleyber Torres and DJ LeMahieu followed with singles before Oswaldo Cabrera popped out to end it.

Isiah Kiner-Falefa was the first baserunner of the game with a two-out single to right in the bottom of the third.

LeMahieu lined a double to center to start the bottom of the fifth, misplayed by Kevin Kiermaier, but the light-hitting bottom half of the lineup couldn’t get anything going, as Cabrera, Oswald Peraza and Kyle Higashioka all struck out.

King gave up back-to-back doubles to Merrifield and Jansen in the seventh, as the Blue Jays extended their lead to 4-0.

LeMahieu singled with two outs in the bottom of the inning and Cabrera hit one to the track in center, but Kiermaier tracked it down.