PITTSBURGH — Mets lefthander Steven Matz delivered a blistering self-assessment on Tuesday, following a 3-1 loss to the Pirates in the first game of a doubleheader.

“I had nothing out there today,” said Matz, who allowed two runs in five laborious innings.

Forced to rely on his changeup, mostly because his fastball command was iffy, Matz took his first loss since April 11. For the first time since that outing, he left the game with his team behind. By the time they chased Matz, the Pirates led 2-0 thanks to RBI singles by Andrew McCutchen and David Freese.

“I was really scuffling from the first inning on. It’s just one of those days,” Matz said. “Tried to battle the best I could. But to only go through five innings in a doubleheader like this, I was pretty disappointed in myself.”

Matz (7-2, 2.69 ERA) did not possess his best stuff one day after his scheduled start was rained out. But he downplayed the impact of the schedule change.

Prior to a no decision in his previous outing, Matz had won seven straight outings.

“You’ve got to command your fastball to make everything else work,” Mets manager Terry Collins said.

Extra bases

Logan Verrett will make a spot start on Saturday as the Mets reshuffled their rotation because of Tuesday’s doubleheader. The Mets considered throwing Verrett on Friday in order to give Matt Harvey an extra days’ rest. But Matz’s struggles forced Collins to use Verrett for two innings of relief . . . Utility man Eric Campbell was eligible for the back end of Tuesday’s twin bill. He was summoned as the 26th man, or the extra player granted to teams for doubleheaders . . . Juan Lagares said he’s not worried that trying to play through a small ligament tear in his left thumb may only worsen the injury. “You never know what’s going to happen,” said Lagares, who remains hopeful about avoiding surgery. “I hope not.” He expects to attempt swinging a bat in the next two or three days, after which the Mets will determine if he can play on . . . The Pirates summoned top pitching prospect Jameson Taillon to make his big league debut against Noah Syndergaard on Wednesday night.