The Mets added some bullpen depth through free agency.

Veteran pitcher Zach Pop, who was designated for assignment by the Mariners last Saturday, has now signed a major league contract with the Mets, as confirmed by The Post’s Jon Heyman.

The 28-year-old showcased a 2.79 ERA across 11 minor league games with Seattle but struggled in the major league, conceding eight earned runs over 5 ¹/₃ innings this season.

In his first rehabilitation appearance following the discovery of a loose body in his left elbow, Sean Manaea reported feeling “great” after pitching 60 times over three-plus innings on Wednesday.

With Double-A Binghamton, he allowed three runs (two earned) on six hits, a walk and three strikeouts.

His elbow had sounded alarms in his previous outing on June 19, and Manaea said his first start back “passed the test.”

He was happy with how he felt, which allowed him to laugh at the results.

“Executing pitches [was a goal], which was not good,” said Manaea, who will pitch in a final rehab game Tuesday and then could return to the Mets on July 13 in Kansas City.

Manager Carlos Mendoza stuck with half of the new-look top of the lineup that he debuted Wednesday night.

This time facing a lefty in José Quintana, Mendoza moved Brandon Nimmo from leadoff to sixth.

But Francisco Lindor, who responded well to shifting out of the No. 1 spot, again was batting second, this time behind DH Starling Marte.

The move worked again in the Mets’ 3-2 win over the Brewers on Thursday night at Citi Field.

Marte singled twice in four at-bats and scoring the go-ahead run in the sixth inning, while Nimmo homered in the second.

“I think it’s more of a case of who we’re playing,” said Mendoza, who has wanted to separate lefties Nimmo and Juan Soto, who also hand an RBI single, in the order against a Brewers team that has three lefty relievers.

But: “Nim, Lindor, Soto,” Mendoza added, “you’re probably going to see that a lot.”

Nimmo’s home run was his 900th career hit, one of 14 players in franchise history to accumulate that many with the Mets.

Edwin Díaz, who picked up his 18th save, struck out two, recording his 491st strikeout as a Met to move into a tie with Tug McGraw for third most all time by a reliever in franchise history.

On a day the Mets moved Blackburn and Dedniel Núñez (elbow sprain) to the IL and optioned Blade Tidwell, they called up righties Rico Garcia, Austin Warren and Justin Hagenman.

Soto was named the NL Player of the Month for June after hitting .322 with 11 home runs, 20 RBIs, a .722 slugging percentage and a .474 on-base percentage in 27 games.

Jonah Tong was the Pitcher of the Month in the Eastern League for a second straight month. The promising righty went 3-0 with a 0.93 ERA in five starts in which he struck out 43 in 29 innings.