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Moment of truth for Sox-killer Happ

BOSTON — There were plenty of reasons the Yankees traded for J.A. Happ in July.

They needed another dependable starter, especially because Masahiro Tanaka and CC Sabathia could have health issues at any time. He had experience pitching in the AL East, having spent time with the Blue Jays. And there was one more thing: Hardly anyone is better against the Red Sox than the 35-year-old lefty.

On Friday, Happ will get a chance to face Boston in Game 1 of the ALDS at Fenway Park.

In his career, Happ is 8-4 with a 2.98 ERA against Boston, and since arriving in The Bronx, he’s 7-0 with a 2.69 ERA and emerged as the Yankees most consistent starter.

The Yankees still opted to start Luis Severino in Wednesday’s wild-card victory over the A’s, and the move paid off with Severino throwing four-plus shutout innings in the win and allowing the Yankees to throw Happ perhaps twice in the ALDS.

He’s faced the Red Sox twice since the trade, giving up just an unearned run in a win at the Stadium on Sept. 18 and then tossing f ive scoreless innings before Steve Pearce hit a grand slam off him with two outs in the sixth 10 days later in Boston.

“We scored four [runs] the last inning we played against him,’’ Boston manager Alex Cora said. “Let’s use that.”

Both Cora and Aaron Boone pointed to Happ’s ability to command his fastball as the key to his success against this team and in this ballpark. And Happ believes the experience of having pitched in a Yankee-Red Sox game at Fenway will be beneficial, regardless of how it ended.

“These games … I’ve learned since I came over here in the short while, can be intense,’’ Happ said of the rivalry. “And I certainly expect a lot more of that.”

Part of that will be up to him, as Happ tries to limit the AL East champ’s potent offense.

“This is a team that won 108 games,’’ Happ said Thursday at Fenway Park after the Yankees arrived from New York. “You don’t see that very often. It’s a team that is probably as dynamic a team as there is in baseball. So… I’m certainly aware of their capabilities.”

Happ’s most recent playoff experience came two years ago with Toronto, when he started twice and pitched effectively each time. He’s going to enjoy this ride, as well.

“The last two weeks have been great,’’ Happ said. “I think you don’t know what to expect. When you get traded to a contender who has a chance to play in October, that’s why you’re playing.”