Steven Matz has been excellent for much of the second half and delivered another strong outing in Sunday’s 2-1 loss to the Braves, but there remains cause for concern with the left-hander, who is dealing with a blister on his middle finger.

The blister, he said, cropped up after the All-Star break and affected him again Sunday, which was one of the reasons Mickey Callaway elected to take Matz out after six innings and 102 pitches — despite Matz having allowed just one run on two hits.

“He’s been battling a blister the last few starts and it was just so sore,’’ Callaway said after the Mets were swept by Atlanta at Citi Field. “He came in after the fifth and was like, ‘Probably one more,’ so it was getting pretty irritated.”

The blister affects him most on sliders and curveballs, Matz said, so he works on them less often between starts.

He didn’t seem bothered by much Sunday, when he mostly dominated Atlanta’s lineup, but the blister forced him out of the game after the sixth. He was replaced by Paul Sewald, who immediately gave up Josh Donaldson’s second homer of the game to start the seventh.

That matched Matz’s only slipup of the game, which came in the second, when Donaldson continued his onslaught on Mets pitching with a leadoff homer to give the Braves the lead.

The ball went just 342 feet down the left-field line, but still left the park.

“He’s such a good hitter and I knew he got it good and got under it, but I looked back on it and it really wasn’t the greatest pitch at 3-2,’’ Matz said. “He’s hurt me in the past and he’s hurt us as a team.”

Adam Duvall followed with a double to center that went over Juan Lagares, who froze on the play.

But Matz responded by retiring the next three batters to keep Atlanta to one run and didn’t allow another hit the rest of his outing.

“[He] was fantastic,’’ Callaway said. “He continues to keep a great tempo, a great pace in between pitches and executes almost every pitch lately, so it’s been fun to watch. He’s been great.”

In his past four starts, Matz has given up just five earned runs in 25 innings, but he admitted the blister hurt him more as the afternoon progressed Sunday.

How that impacts him going forward remains to be seen.

“It’s been coming on in the second half and it flares up off the slider,’’ Matz said. “It’s just something I have to manage. … Today it got pretty sore toward the end of the game.’’