NEW YORK -- Nothing this season has gone according to plan for the New York Mets. Finally, on Wednesday night, they benefited from the unexpected.

Travis d'Arnaud hit a two-run homer during a three-run first inning, and Robert Gsellman, pitching hours after being recalled from Triple-A Las Vegas, was credited with his first complete game as the Mets beat the Philadelphia Phillies 6-3 in a game shortened to 5 1/2 innings by rain at Citi Field.

Such a result was hard to conceive earlier in the night for Mets manager Terry Collins, who got a foreboding weather forecast when he visited the umpires just before first pitch.

"They said at home plate that the rain was coming, they thought, about 8:30," Collins said. "We have not played the fastest games, so I thought we were going to have a tough time getting five in."

Instead, Gsellman rewarded the Mets for staking him to the early lead by offering up the kind of efficiency New York expected but rarely received from him or the rest of the ballyhooed rotation.

New York's starting staff, which consists entirely of 20-somethings, entered the season with high expectations, but injuries and ineffectiveness have befallen every projected starter except ace Jacob deGrom. Mets starters have a 5.17 ERA, which would be the second worst in franchise history behind the expansion 1962 team, whose rotation posted a 5.18 ERA for a 120-loss club.

Gsellman, who helped the Mets reach the National League wild-card game last season by going 4-2 with a 2.42 ERA in eight games (seven starts), has fit right in this year by going 6-6 with a 5.34 ERA, spending a month on the disabled list with a hamstring injury and enduring two demotions to Las Vegas.

"Every time you get sent down, it's very eye-opening," Gsellman said. "You learn a lot and you just come back a little hungrier."

Gsellman carried a three-hit shutout into the sixth, when an inning-opening error by third baseman Asdrubal Cabrera helped create the Phillies' three-run rally. The 24-year-old right-hander, who was charged with three runs (two earned), allowed five hits and one walk while striking out four.

Most impressive of all, Gsellman threw a first-pitch strike to the first 13 batters he faced Wednesday and 19 out of 24 overall. He allowed hits on the first two pitches of the game but wriggled out of the jam and retired 13 of 14 batters between the first and fifth.

"When I talked to him this afternoon about pitching today, he said, 'I was hoping I was going to get the chance,'" Collins said, "I think he has come back with a little different frame of mind, that I've got to work myself into the rotation somehow."

Cabrera had three hits, including an RBI single immediately before d'Arnaud's homer in the first for the Mets (60-79), who won the three-game series for their first series victory since taking two of three from the Phillies Aug. 11-13. Gsellman added an RBI single in the second, and Brandon Nimmo lofted sacrifice flies in the third and fifth.

Cesar Hernandez had three hits for the Phillies, including an RBI double in the sixth. Nick Williams hit a one-out, two-run homer later in the inning for Philadelphia, whose comeback hopes were squelched when the teams were pulled off the field at 9:03 p.m. EDT with one out in the bottom of the sixth and a heavy rain falling.

"It's a shame we got banged, because we started mounting a comeback," Phillies manager Pete Mackanin said. "But it is what it is."

The game was officially called after a 58-minute delay.

"I know early this morning, obviously, the percentages were a little different," d'Arnaud said, referring to the weather forecast. "Gsellman did a great job of getting ahead of every single hitter and working really fast, and we were able to get this game in."

Phillies right-hander Nick Pivetta (5-10) took the loss after allowing six runs on 10 hits and no walks over five innings. He struck out five.

"Threw strikes, but not quality strikes," Mackanin said of Pivetta. "Too many bad pitches."

NOTES: The rain-shortened game was the first for both teams since the Mets beat the Phillies 5-4 in seven innings on Sept. 21, 2013. ... Mets RHP Matt Harvey, who was scheduled to start on three days' rest Wednesday before being scratched late Tuesday night due to the weather forecast, will start the series opener against the Cincinnati Reds on Thursday. ... Mets OF Michael Conforto (left shoulder) underwent surgery Wednesday to repair a torn posterior capsule. He is expected to need six months to recover. ... The Phillies traded RHP Juan Nicasio to the St. Louis Cardinals in exchange for minor league INF Eliezer Alvarez. ... Phillies CF Odubel Herrera, who has a 19-game hitting streak, did not play.