Jose Reyes of the New York Mets looks on after...

Jose Reyes of the New York Mets looks on after striking out looking in the second inning against the Pittsburgh Pirates at PNC Park on Saturday, May 27, 2017, in Pittsburgh. Credit: Getty Images / Justin K. Aller

PITTSBURGH — Terry Collins leaned back in his chair Saturday night, the exasperation bubbling in his chest forcing him to let out a deep breath. As if by reflex, he extended his arms and turned his palms upward, a signal of momentary surrender.

“I’m out of explanations,” the Mets’ manager said as he surveyed the ruins of a 5-4 loss to the Pirates in 10 innings, the product of his team’s latest bullpen implosion.

Questioned by fans, scrutinized by his own front office, the longest-tenured manager in Mets history took a match to the book of bullpen management as his team fought to preserve a slim lead against the late-charging Pirates. And for once in this recurring nightmare of a season, it worked.

Then the ninth inning rolled around and Collins placed the ball in the hands of closer Addison Reed, tasking him to protect a one-run lead. “I felt pretty good when I gave him the baseball,” said Collins, who soon would feel ill.

Reed blew a save opportunity for the second time this season, allowing a tying hit by John Jaso, who also delivered the winning single off Josh Edgin in the 10th.

With that, the Mets absorbed yet another body blow of a loss, one that called attention to a bullpen that is reeling from a heavy workload.

“This is unacceptable,” said Reed, whose ERA rose to 3.51. “This is not how I am expecting to throw the ball. This is not what I’m getting paid for. The way I’m throwing the ball right now is absolutely unacceptable, there’s no other words for it.”

Reed brushed off concerns about his workload after his 26th appearance, but Collins said it’s “my fault” and that the added wear could be a factor in Reed’s struggles to replace the injured Jeurys Familia.

A stalwart last season when he posted a 1.95 ERA in 80 games as the primary setup man to Familia, Reed has struggled with his command while trying to fill a new role.

“We’ve had so many close games,” Collins said. “We’ve asked him to pitch quite a bit. A year ago, he just didn’t miss a spot. He was down in the zone, both sides of the plate. Pitched in. Right now, he’s leaving balls up in the hitting area.”

Reed hardly was alone for the blame in the Mets’ 11th loss in 15 games.

Travis d’Arnaud knocked in a pair of runs and homered, finishing a triple shy of the cycle, and Jay Bruce and Lucas Duda hit solo homers. But the Mets (20-27) paid dearly for leaving 10 men on base and going 1-for-7 with runners in scoring position.

Zack Wheeler allowed three runs in six innings in an unspectacular start, but he left with the lead. He was to start the seventh, but a blister on his right middle finger ended his night.

“It formed in the third inning but I honestly didn’t feel it until I looked down on it,” said Wheeler, who was pulled after 94 pitches.

So began an unorthodox series of moves that worked. Collins needed six outs to reach Reed in the ninth inning. With Paul Sewald still recovering from a three-inning stint on Thursday, Neil Ramirez entered with his 10.32 ERA and survived a leadoff double when lefthander Jerry Blevins bailed him out. Overworked Fernando Salas got a couple of great defensive plays in the eighth.

Then Reed blew the game in the ninth and Collins used rookie Tyler Pill in the 10th. He had been promoted the day before. Pill departed his major-league debut with two outs and the bases loaded thanks to a hit, a hit batter and a walk.

Collins summoned Edgin to face Jaso, who had one hit in his last 30 at-bats against lefties. It didn’t matter. Jaso drove the winning single to deep rightfield, and with that, the evening was shot.

Collins turned 68 on Saturday, but there was nothing to celebrate. He returned to his office to find a printed email — news of Yoenis Cespedes’ setback after his first rehab game. Then he spent the next six minutes rehashing the previous three hours, most of them brutal.

“No matter what we do,’’ Collins said, “it’s not working.”