MLB

Jeremy Hefner, Mets mauled by Phillies

The Mets hosted the Home Run Derby Monday at Citi Field; and last night they put on an encore, though not one their fans shouted for, as they gave up three round-trippers in a 13-8 battering by the Phillies.

It was a nightmarish start to the second half of the season — and one has to wonder when Jeremy Hefner has nightmares, are they of Phillies?

After closing the first half 16-10 to build confidence and buzz, the Mets kicked off the second half by getting kicked around in front of

35,021 hot, cranky fans at Citi Field on an evening that saw 95-degree heat at first pitch. They Mets made three errors and fell behind 11-0 in the third inning, with Hefner (4-7) digging them in a hole too deep even for their spirited rally to dig out of.

The emerging right-hander — who had been as hot as the weather the past month-and-a-half — has struggled more at the hands of Philadelphia than any other pitcher. Hefner never gave the Mets a chance right from the start, as he was hammered for eight runs — all earned — in just two-plus innings. And, as much as it strains credulity, that was actually an improvement.

He had allowed seven runs in his last home start against the Phillies without recording a single out on Sept. 20, 2012. That’s 15 runs in his last two-plus home innings against Philadelphia, and his 13.75 ERA is the worst of any active pitcher with at least four starts against the Phillies.

And as good as Hefner had been of late, last night — betrayed by some shabby Mets defense — he went back to the early-season version who couldn’t finish off hitters. He needed 20 minutes and a mound visit from manager Terry Collins just to get out of the first inning down 4-0, cheered sarcastically by the sweltering fans.

Hefner allowed five straight one-out hits by Chase Utley, Domonic Brown, Darin Ruf, Delmon Young and finally John Mayberry Jr., before he finally retired Carlos Ruiz to derisive applause and needed 10 pitches to catch opposing pitcher Kyle Kendrick (9-6) looking. It got far worse in the third, when the Phillies erupted for seven more runs.

Hefner saw Brown crush his 0-2 curveball into the Pepsi Porch in right, then gave up an RBI single to Young and an RBI double to Mayberry before Collins mercifully pulled him.

But that hardly stopped the bloodletting. Ruiz greeted reliever Greg Burke by doubling to right to plate Mayberry and close the book on Hefner. Burke allowed four earned runs in 2 ²/₃ innings, Josh Edgin a run in one-third of an inning.

Marlon Byrd committed an error in the third, while Omar Quintanilla had errors in the fourth and sixth. Byrd did hit a mammoth three-run shot to cut it to 11-3 in the fourth, and the Mets added a run in the fifth and two in the sixth before David Wright launched a two-run shot in the ninth — his 14th of the year. But it was all cosmetic, and there was no way to beautify a game this ugly.

It was a sobering beginning to the second half and a shocking outing for Hefner, whose 1.76 ERA since June had been the best in the majors.

“He’s grabbed this opportunity to show, ‘Hey, pitchers like myself can succeed in the major leagues if we locate, ” Collins said before the game. “That’s what he’s doing. Right now Jeremy’s doing a great job of it.

“He’s pitching with great confidence. When he makes mistakes, he’s making mistakes down in the zone. He’s not making mistakes out over the plate, so you’re not seeing as many balls hit hard.

“He made a couple tweaks in his delivery. His velocity’s up; he’s not just 88, 89, he’s 91, hit 94 several times. He now has a good enough fastball you have to protect it; now you’re going to get swings on other pitches because you’ve got to get the bat started on the fastball, which made a big difference. He’s throwing strikes with all his pitches and he’s pitched inside which has been a big difference.’’

brian.lewis@nypost.com