Mark Leiter Jr. hasn’t even been a Yankee for a week, but the club has leaned heavily on the second-generation hurler.

The 33-year-old took the mound on Sunday against the Blue Jays with two outs and one man on in the ninth inning of a three-all game, which had just stalled for an hour and 49 minutes after storm clouds engulfed Yankee Stadium.

It hardly seemed to affect Leiter, who recorded three strikeouts and gave up no hits to set up DJ LeMahieu’s walk-off single in the Yankees’ 4-3, 10-inning victory in their series finale against Toronto.

“He likes the action,” manager Aaron Boone said. “He likes being out there when it counts. Seems to have a really good competitive nature to him. Obviously, the split is a really good pitch. And today going through the meat of the order, you got [Vladimir Guerrero Jr.] there leading off the 10th, runner on second, here we go. We considered for a minute walking him, but then you’re like, ‘Man, then [Steward] Berroa probably stays in, they brought him over.’ So we had to go after him.

“Gets a big out there, obviously then [George] Springer comes into play, big out there. So just a really good job of continuing to make pitches and a lot of high leverage ones today.”

After striking out Joey Loperfido to send the game to extra innings, Leiter got Guerrero to whiff at two pitches before the Blue Jays slugger lined out to center.

The Yankees successfully challenged for a hit by pitch call on Daulton Varsho, but Leiter registered two strikes on 92-mph sinkers before his sinker KO’d Alejandro Kirk.

LeMahieu finished the job to give the Yankees their first home series win since the first week of June.

“I felt more like myself today,” Leiter said when asked if his splitter felt sharper. “That’s a role, like when you’re in those high-leverage spots, you got to make pitches and you need to make your best pitches when your backs are against the wall. So just kind of staying calm and knowing that you’re always a pitch away and just one pitch at a time to fight through it.

“I think it’s a good mindset to have and I knew that if we didn’t give one up we had a good chance to win.”

Leiter, who the Yankees acquired from the Cubs in exchange for infielder Ben Cowles and pitcher Jack Neely, talked about trying to stay mentally ready to play and not let anything get in the way of that during the rain delay.

It was Leiter’s fourth outing with the Yankees — all of which have been wins.

With his signature splitter, Leiter recorded five balls, got four swings and misses and one called strike.

“I thought it was the best day yet,” Boone said. “Big reason why we got him is that pitch. I thought today was the most crisp it’s been in any of his outings.”