PHILADELPHIA — Maybe it’s a sign of the apocalypse. 

No, not the smoke-filled swath covering much of the East Coast on Thursday; that was expected. 

Instead, it was the Mets opening the second half of their season with a 4-1 win over the Phillies. 

Powered by solo homers from Francisco Alvarez — who had two — and Brett Baty, as well as a strong start by Christian Scott, the reeling Mets avoided falling 18 games under .500 for the first time this year. 

After the start of the game was moved up an hour due to air quality concerns caused by Canadian wildfires — which forced both teams to shorten their pregame routines after their truncated All-Star break — the Mets played an unusually solid game. 

“I’m not gonna lie: Towards the end, it got a little thick,” Scott said of playing through the smoke. “It felt like breathing in some metal. … A little spoonful of adversity never hurt anybody.” 

The Mets have downed plenty of adversity this season, and there’s little chance of a turnaround, especially as they’re expected to sell at the Aug. 3 trade deadline. 

They also have the toughest schedule the rest of the season and start the second half visiting second-place division rival Philadelphia and NL Central leader Milwaukee before hosting the NL West-leading Dodgers and NL East-topping Braves. 

But they can try to avoid being blown away by what’s ahead of them over the final two-plus months of the season. 

“We’re well aware we’re staring down one of the hardest schedules in baseball for the second half,’’ interim manager Andy Green said. “We should relish that, like that and rise up and meet that. I don’t think there’s another attitude to take.” 

It’s performances like what they got from Alvarez and Baty at the bottom of the lineup and a promising young starting pitcher like Scott that could boost them. 

On Thursday, as the Philadelphia skyline slowly disappeared in the distance due to the worsening conditions, the Mets took the lead in the top of the third on Alvarez’s first homer of the night, a one-out shot to dead center. 

Baty added his fifth of the year, leading off against Aaron Nola in the seventh. 

Alvarez followed in the next at-bat with his second of the game to end Nola’s night. 

On the other side, Scott retired 10 of the first 11 batters he faced before Bryce Harper doubled down the right field line with one out in the bottom of the fourth. 

Brooks Raley replaced Scott after just 79 pitches to face Harper. 

Harper reached on a four-pitch walk, but Raley got Marsh swinging to end the threat. 

The Phillies got to Luke Weaver with two outs in the eighth as Trea Turner took him deep to make it 3-1. It snapped Weaver’s 27-inning streak without allowing a home run. 

The Mets got the run back when A.J. Ewing doubled in Jared Young in the ninth to finish off a strange afternoon and evening. 

“I didn’t think it was bad till the last couple innings,” Baty said. “My eyes were burning and itching a little bit. [Carson] Benge said it felt like you were sitting by a campfire. … It was fun … but it didn’t feel great playing ball with it.” 

The results, though, were pretty good for a change.