First Noah Syndergaard got scratched. Then Matt Harvey got strafed.

The Mets turned to Harvey on Thursday morning when Syndergaard was a late scratch with a tired arm and sore biceps. But it was Harvey who got worn out and chased in the fifth inning of a 7-5 loss to the Braves before 23,243 at Citi Field.

“Things were just pretty tight mechanically. Overall it felt tight on the mound and couldn’t get loose throughout the start. Just kind of a rough day,” Harvey said.

Harvey (2-1) allowed five hits and six earned runs in 4 ¹/₃ innings, issuing a career-high five walks and striking out just one after he was thrown into the fire on short notice, for his second straight start.

“It’s different, something I’m not used to,” he said. “I needed to do a better job of being ready. I was expecting to pitch [Friday], I had a big workout [Wednesday], so body-wise it just tightened up and I wasn’t physically prepared for starting. Obviously it’s happened before once, and I need to be ready for it to happen again. I got the call and I just needed to be ready.”

Harvey had prepared Tuesday and Wednesday as if he were starting Friday in Washington. Though the Mets knew Wednesday that Syndergaard was sore, Harvey wasn’t told anything until he got a call from pitching coach Dan Warthen at 10 a.m., with first pitch slated for 1:10 p.m.

“I had no idea. I prepared [Wednesday] to start on Friday. So having those workouts I did, the throwing I did, I just definitely wasn’t prepared. But it’s our job to be ready at any time and I didn’t do a very good job of that,’’ Harvey said. “I was just a little tight from the workout [Wednesday] and not anticipating pitching, so I think being more careful with that moving forward will help.”

Harvey started off strong, hitting 94 mph in a scoreless first. But his velocity dropped to the low 90s and he walked three in a two-run second before getting chased in the fifth by Kurt Suzuki’s three-run shot and leaving the game trailing, 6-2.

“I know he got out of his mechanics which caused him to lose a little bit of command,” catcher Travis d’Arnaud said.

“I saw a guy whose mechanics were a little bit askew. … All of a sudden, command was gone, velocity was down, sharpness was down,” said Terry Collins, not willing to concede the late change impacted Harvey. “I told Matt — and I’ll stand by it — this is two times in a row we’ve asked him to step up and pitch when he wasn’t expected to. That’s hard to do at this level, as these guys have routines that’re important. But he just wasn’t sharp, and we have to get him going.

“When I talked to Matt [Thursday] morning and asked could he pitch, he said ‘Absolutely. It’s my day to pitch anyway.’

“Now that being said, that’s how big league pitchers are supposed to talk. … You can assume [it affected him], but assumptions are what they are. You can make them, but he’s the only one who can answer that.”