The Yankees added to their bullpen earlier in the week when they picked up Zach Britton from Baltimore and Saturday they lost a reliever when they traded another lefty, Chasen Shreve, to St. Louis.

The trade of Shreve opens a spot on the roster for Sunday’s starter, J.A. Happ, who arrived Saturday after being acquired from Toronto. In exchange for the 28-year-old Shreve and right-hander Giovanny Gallegos, the Yankees received first baseman Luke Voit and international bonus pool money.

Voit, 27, was 2-for-11 with a homer in eight games with the Cardinals this season and spent most of the year with Triple-A Memphis. The 26-year-old Gallegos pitched in 20 games for the Yankees over the past two seasons and was at Triple-A Scranton/Wilkes-Barre.

“I knew we had to make a move,’’ an emotional Shreve said after the Yankees split a doubleheader against the Royals on Saturday in The Bronx. “I just didn’t know what it was gonna be. I had prepared myself for it. I love it here. I’ve been here four years and it’s gonna suck to leave.”

Shreve pitched an inning and gave up a run in the first game of the doubleheader, a 10-5 loss.

It was the first time he had been scored upon since July 7, as he rebounded from a tough first two months of the season. Heading into Saturday, Shreve had allowed just two runs in his previous 11 outings over 11 innings for a 1.64 ERA.

And he picked up a key save last Saturday after Aroldis Chapman imploded against the Mets while trying to protect a four-run lead. Shreve entered with the bases loaded, no one out and the Yankees up by two runs. Shreve got a double play and a comebacker to let the Yankees escape with a victory.

The Yankees’ bullpen now consists of a pair of southpaws — Chapman and Britton — as well as Dellin Betances, A.J. Cole, Chad Green, Jonathan Holder, David Robertson and Adam Warren.

Shreve pitched in 40 games for the Yankees this season. He came to the Yankees prior to the 2015 season, when they sent former prospect Manny Banuelos to Atlanta for Shreve and David Carpenter. Shreve appeared in 180 games for the Yankees, although he was not on the postseason roster last year.

“I’ll have a good opportunity over there,’’ Shreve said of St. Louis. “But I’m gonna miss these guys.”