The Mets can’t hit lefties, can’t hit at home or in the clutch. Their slump is so bad that even one of the few big hits they got in a humbling 7-3 loss to the Pirates — Jordany Valdespin’s ninth-inning homer — left heads shaking and a sour taste, thanks to yet more showboating by the youngster.

Shaun Marcum (0-3) coughed up six runs in 4 2/3 innings. He was roughed up for three runs in the second and fifth innings and even took a hard shot off his left hand.

“It’s fine right now,’’ said Marcum, who manager Terry Collins said is essentially going through spring training now. “I feel good. I’m just not making pitches. I got to get back to locating and getting the ball down in the zone. I’m missing location.’’

The Mets went 1-for-12 with men in scoring position, and David Wright — who fouled a ball off his left knee in the first inning — admitted the Mets are not just struggling but pressing.

“We’re in one of those ruts right now where it just doesn’t seem like — short of that ninth inning — we can sustain, get a few hits in a row,’’ said Wright, who insisted his leg is OK. “It seems like we have one or two opportunities to score runs, and if we don’t do it then we don’t do it.

“I think guys are pressing a little bit — and rightfully so. Everybody wants to be the guy that gets that big hit that breaks the spell, but in doing so, you put too much pressure on yourself sometimes.’’

In their last 11 home games, the Mets have averaged only 2.6 runs, hit just .198 and been held to three runs or fewer nine times. Last night Pittsburgh lefty Wandy Rodriguez (3-2) held them to just one run — backup catcher Anthony Recker’s fifth-inning solo homer — in six strong innings.