PITTSBURGH — If the Mets were going for efficiency, they can say that they achieved it. In the space of just six hours on Tuesday they squeezed in 18 innings of offensive futility on the way to a pair of migraine-inducing defeats.

In both ends of a doubleheader — both 3-1 losses to the Pirates — the healthy survivors of a Mets offense that has been besieged by injuries appeared incapable of providing resistance.

“I’m a little bit lost at the plate right now,” said Yoenis Cespedes, the $27.5 million slugger who insists that a sore hip isn’t behind a sudden drop in production in what had been a monster season.

Of course, he hasn’t been the only offender, and for that the Mets find themselves facing the consequences. After beginning a 10-game road trip by taking two of three against the Marlins, the Mets turn to Noah Syndergaard in hopes of avoiding a three-game sweep.

“We’ve got some guys struggling, there’s no question, and they’re huge pieces,” manager Terry Collins said during the brief interlude between a pair of losses that dropped the Mets to 31-26.

Collins didn’t need to name names to cast a spotlight on the most conspicuously cold bats in his lineup that totaled only nine hits in the two games The list includes Curtis Granderson, Michael Conforto and Cespedes. Their struggles have only become more harmful with David Wright, Lucas Duda and Travis d’Arnaud out of commission.

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“I think we’ll turn it around,” said Neil Walker, whose sweet homecoming was paired with the bitterness of two losses. “This is way too good a hitting group.”

For now, they don’t look like it. After blasting their way through the opening weeks of the season, the homers have dried up, and the Mets’ inability to score runs in other ways have become an open wound.

Cespedes returned to the starting lineup for the first time since Friday. Since then, hip soreness had kept him to one pinch-hitting appearance. He started both games, reassuring Collins between them that he was healthy to go.

But the slugger went 0-for-7 with a walk, plunging himself deeper into a 3-for-35 skid. It comes as the Mets desperately search for someone to resuscitate the offense, though he insisted it hasn’t added to his frustration.

“No,” he said. “I’m not Superman.”

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Conforto doubled, though it was his only hit in two games. And when he was presented with a big spot — with the bases loaded in the opener against former Met Jonathon Niese — he struck out. Conforto is in a 4-for-40 tailspin.

Granderson’s 10th homer provided the Mets with their only run in the first game. But he has shown only fleeting signs of turning around a disappointing season in which he’s hitting .204.

Granderson has started the month of June just 3-for-24. Shortstop Asdrubal Cabrera went hitless in both games. He is mired in an 0-for-15 slide.

“There’s no instant fix, no scramble the lineup, take this guy out,” Collins said. “It’s a total package. You’ve got to get everybody going and we’re not hitting as a group.”

Mets starters Steven Matz (7-2), who suffered his first loss since April 11, and Jacob deGrom (3-2) delivered unspectacular outings, though both would have been good enough had they received support.

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Matz went just five innings but allowed two runs, not good enough against Niese, who tossed seven shutout innings. Traded this winter for Walker, Niese admitted to some extra motivation.

In the nightcap, deGrom allowed three runs in six innings, though he racked up an encouraging nine strikeouts and kept the Mets within striking distance. But just as it was so often last season — when injuries gutted the lineup — a grueling day ended with a member of the rotation playing the part of the good soldier.

“Everybody’s grinding, trying to do their best,” deGrom said. “It’s just a tough stretch right now.”