The Mets had originally decided to pitch Matt Harvey on three days’ rest on Wednesday night against the Phillies in his second start off the disabled list. A poor weather forecast and a bout of common sense caused the team to move Harvey to Thursday.

Robert Gsellman got the start instead and allowed three runs (two earned) in a six-inning, complete-game victory as the Mets beat the Phillies, 6-3, in a rain-shortened game at Citi Field.

Most of the game was played in rain. Umpires halted play at 9:03 p.m. with one out in the bottom of the sixth. The game was deemed final at the stroke of 10 after a wait of 57 minutes.

Gsellman (6-6) allowed singles to the first two batters of the game and then only one more hit through five scoreless innings as the Mets built a 6-0 lead against Phillies starter Nick Pivetta (5-10), who allowed 10 hits in five innings.

Asdrubal Cabrera had an RBI single and Travis d’Arnaud smacked a two-run homer to right as the Mets took a 3-0 lead in the first. It was d’Arnaud’s 11th home run.

Gsellman made it 4-0 with an RBI single in the second. Brandon Nimmo had sacrifice flies in the fourth and sixth.

Gsellman gave up three runs in the sixth inning, only two of which were earned. Cabrera, playing third base, threw away Ty Kelly’s leadoff grounder for a two-base error. Cesar Hernandez drove in the Phillies’ first run with a single. Two batters later, Nick Williams made it 6-3 with a two-run homer to right.

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Because there was no top of the seventh, Gsellman was credited with his first career complete game.

Extra bases

Michael Conforto underwent surgery in Los Angeles to repair a tear in the posterior capsule in his left shoulder. Recovery time is six months, according to the Mets . . . Noah Syndergaard will make a rehab start Thursday for the Brooklyn Cyclones against visiting Staten Island.