Aaron Boone was asked to describe his comfort level when J.A. Happ toes the rubber.

“It’s one of those days you look forward to,” the first-year manager said before Thursday night’s series opener against the Tigers.

Or, at least, it had been until he jinxed his left-hander.

Happ’s string of strong outings since coming over to the Yankees before the July 31 non-waiver trade deadline was snapped, as he had by far his worst outing in pinstripes. He was tagged for five earned runs and failed to make it through the fifth inning in an ugly 8-7 loss to the Tigers in The Bronx that saw Dellin Betances touched up for backbreaking ninth-inning home runs by Victor Martinez and Niko Goodrum.

In his first five starts with his new team, the 35-year-old Happ hadn’t allowed more than three runs and had gone six innings or more four times. But he was a different pitcher this time. Happ was hit hard by a mediocre Tigers lineup, raked for 10 hits and three home runs in a no-decision while striking out three. Twice, he was given leads, and twice he surrendered two-run homers to give the lead right back.

“To not be able to hold a lead, I take a lot of pride in that,” Happ said. “It’s not something I give up a lot. So tonight was very frustrating in that sense, giving up the lead.”

It was apparent early Happy wasn’t at his best. Jeimer Candelario turned around Happ’s fifth pitch of the evening, a 93-mph fastball, for a leadoff homer. Ronny Rodriguez and Martinez also went yard, marking the first time this season the southpaw allowed three homers in one game. The 10 hits he gave up equaled a season-high. Boone had raved about Happ’s ability to pitch off his fastball, but all three long balls came on the heater.

Happ didn’t get a lot of help from his defense, either. Gleyber Torres booted a potential double-play ball in the second inning and in the fourth the Yankees had Goodrum picked off between second and third, but allowed him to get back to second safely.

“He had to throw more pitches than he probably should’ve,” Boone said. “If we complete some plays behind him, it makes it a little easier on him.”

Perhaps the poor performance shouldn’t have been such a surprise. Happ entered with poor numbers this season against the Tigers, 0-1 and a 9.28 ERA this year in two starts as a member of the Blue Jays. That trend continued Thursday, while another — his excellence so far as a Yankee — did not.

“I give them credit, really,” Happ said. “There’s no excuses. The results are what they are. They had me and it wasn’t my night tonight.”