Mets rightfielder Jay Bruce greets leftfielder Michael Conforto at home after Conforto...

Mets rightfielder Jay Bruce greets leftfielder Michael Conforto at home after Conforto hit a three-run home during the fifth inning of the game at Citi Field on Sunday, Sept. 9, 2018. Credit: Joseph D. Sullivan

With rain falling at Citi Field into the afternoon — and continuing throughout the Mets’ 6-4 win over the Phillies — the Mets scratched Jacob deGrom from his scheduled start Sunday, opting for a de facto bullpen day instead.

Hours before the first pitch, manager Mickey Callaway warned that with consistent rain expected, the Mets might make a late switch. The reason: They didn’t want to risk wasting deGrom, a leading candidate for the National League Cy Young Award, on a potentially rain-shortened start.

They made the call about 40 minutes before the scheduled 1:10 p.m. start time, which was delayed until 1:37 p.m.

“We knew we were going to get delayed and we knew the outlook wasn’t great,” Callaway said. “We talked internally about what we thought was best, and we approached Jacob about it and said, ‘Hey, there’s a good chance you could start this game, it could be one inning or two innings, and then we could get a long delay and probably [postponed] for the rest of the day.’ That was the forecast at the time. We got his input on everything as well.”

Callaway said the Mets would have made the same decision even if deGrom weren’t in pursuit of the Cy Young. He is scheduled to start Monday at Citi Field against the Marlins, and the one-day delay shouldn’t affect how many starts he makes the rest of the season. He still can have five more outings: Monday vs. Miami, Saturday at Boston, Sept. 20 at Washington, Sept. 25 vs. Atlanta and Sept. 30 vs. Miami.

By the way, rain is expected all day Monday.

As the teams played through a drizzle, Corey Oswalt got the start and allowed two runs — both on Rhys Hoskins’ line-drive homer in the first — in three innings. Of Oswalt’s nine major-league starts, this was his second in place of deGrom on short notice. He also got the ball June 29 in Miami when deGrom had to address a family issue.

Four Mets relievers — Drew Gagnon, Eric Hanhold, Drew Smith and Seth Lugo (save) — combined to allow two hits and two runs in six innings.

“They all knew they needed to be on alert from inning one,” Callaway said.

Oswalt was happy to make the spot start, especially if it was for the greater good of deGrom’s Cy Young chances.

“It’s been crazy — the stuff he’s doing, the numbers he’s putting up. Every time he goes out there, he’s dominating,” Oswalt said. “It’s been really fun to watch.”

The game turned in the fifth. Jeff McNeil had an RBI single to tie it and Michael Conforto (2-for-5) smacked a three-run home run to give the Mets a 5-2 lead.

McNeil had three hits for the second game in a row and for the fifth time in 44 career games. Conforto’s four RBIs tied his career high.

Even without their ace, the Mets (65-77) took the series rubber game from the Phillies (74-68), who are threatening to fall out of the NL East race. They are 4 1⁄2 games behind the Braves.

The Mets are 10-6 against Philadelphia, 19-24 against the rest of the division and 4-12 against the Braves. They have one more series to play spoiler against the Phillies, Sept. 17-19 in Philadelphia.

“We’ve obviously played well in the win-loss column, but they’re a big rivalry, I think our guys get pumped up to go play them and we play solid baseball against them,” Callaway said. ”We’ve gone out there and we’ve scrapped really hard against them every time we played them.”