NEW YORK — On a pitching staff packed with young arms, Jeremy Hellickson has been the one experienced starter Philadelphia could count on all season.

Not this time against the hot-hitting New York Mets.

Yoenis Cespedes clocked a three-run homer off Hellickson, and Kelly Johnson had a pinch-hit grand slam as the Mets routed the Phillies 12-1 on Saturday night behind Noah Syndergaard.

“Bad pitching,” manager Pete Mackanin said. “Tonight was embarrassing.”

Asdrubal Cabrera homered for the third time in two games, a two-run drive that put New York ahead against Hellickson (10-8). Neil Walker added his 23rd of the season to match a career high, giving the Mets four homers for the second consecutive night in a blowout of Philadelphia.

The Mets have won 12 of their past 14 series with the Phillies.

“It’s like they know what’s coming,” Mackanin said. “They just seem to feast on our pitching.”

Hellickson, who had won four straight decisions and six of his last seven, allowed a three-run shot to Cespedes that made it 5-1 with two outs in the fourth inning.

Johnson’s drive off Michael Mariot in a six-run seventh was his fourth pinch-hit homer this season. It gave the Mets grand slams in consecutive games for the first time since Carlos Beltran hit both in July 2006.

Philadelphia had won Hellickson’s previous six starts.

“They’re an aggressive lineup. They’re hot right now. They’re not missing too many mistakes,” the 2011 AL Rookie of the Year said. “Just one of those nights. Didn’t really have much.”

Syndergaard tossed two-hit ball over seven innings and Alejandro De Aza hit a two-run double for the Mets, who won for the sixth time in seven games as they attempt to make a push in the NL wild-card chase.

Jose Reyes and Cabrera each had three hits, once again providing a spark from the top two spots in the lineup since both came off the disabled list. Mostly healthy at last after lagging through much of the summer as one of baseball’s weakest offenses, the Mets have totaled 31 runs while winning their past three games.

New York has posted at least nine runs in three straight for the first time since June 2012 — and scored nine or more in successive home games for the first time since September 2008.

“It looks like a completely different team,” manager Terry Collins said. “The energy is just different in the room right now.”

Syndergaard (12-7) chipped in with a long double and is 3-0 with a 1.31 ERA in his last three starts.

The only damage against him came on Freddy Galvis’ homer in the third, and the big right-hander improved to 4-0 with a 1.37 ERA in four career outings against the Phillies.

“No offense to talk about, other than Freddy’s home run. Nice to see that. But after that, nothing,” Mackanin said.

THE NEW TEACHER

A.J. Ellis joined the Phillies before the game, caught a couple of bullpens and asked reporters how to pronounce the name of new teammate Jerad Eickhoff. Ellis is set to make his first start for Philadelphia on Sunday when he catches struggling young right-hander Vince Velasquez. The 35-year-old backstop, obtained Thursday from the first-place Dodgers in a surprising trade for longtime Philadelphia catcher Carlos Ruiz, was brought in to mentor the team’s developing pitchers.

“The waves of emotion are getting farther and farther apart, which is a good thing,” Ellis said. “I’ve started feeling re-energized, filled with a sense of purpose as to why I’ve been placed here and why this is where I need to be at this time, so I’m excited about that. And I’ve got huge shoes to fill, I know that.”

SHORT STAY

To open a roster spot for Ellis, the Phillies optioned touted catching prospect Jorge Alfaro back to Double-A Reading after he spent one day in the big leagues on the bench.

UP NEXT

Phillies: Velasquez (8-6, 4.31 ERA) has lost three straight starts and is winless in seven outings since July 8.

Mets: RHP Robert Gsellman makes his first major league start in the series finale Sunday. He won his debut Tuesday at St. Louis with 3 2/3 scoreless innings in relief of injured Jonathon Niese.