After one of the biggest and most uplifting wins of their season, the Braves laid an egg Sunday against the Mets in the latest of many disappointing losses.

More specifically, rookie starter Mike Foltynewicz and a pair of relievers laid big eggs, and gave up big blasts.

Jace Peterson had a three-run homer in the second inning and the Braves staked Foltynewicz to a 5-1 lead through the top of the third and an 8-3 lead through the top of the fourth, but he blew nearly all of both leads before exiting with one out in the fifth.

Relievers Brandon Cunniff and Luis Avilan fanned the flames from there, each serving up a multi-run homer in a 10-8 loss at Citi Field that gave New York a series win and dropped the third-place Braves back to 3 ½ games behind the National League East-leading Mets.

“I just didn’t have it today, period,” said Foltynewicz, whose ERA climbed to 5.19 after he was charged with nine hits and six runs (five earned, one on a Christian Bethancourt passed ball). “When a team gives you a five-run lead like that you’ve got to take advantage of it. I didn’t do that today. Just left everything up, really, from the start. Fastballs, curveballs, slider, even change-ups were up today.”

His pitches were up, and the Braves were down.

It was the third time in 11 games that the Braves lost despite scoring eight or more runs, which is three times as many games as they lost when scoring that many during the previous five seasons combined. They were 103-1 in such games during that period, and are 7-4 this season.

Manager Fredi Gonzalez sounded as worn down and exasperated afterward as he has after any game since taking over as manager after the 2010 season. The Braves hit .300 and scored 60 runs in their past 12 games, but won just four of them, primarily because of a 4.91 ERA in that period. They had 14 hits Sunday.

“Proud of (the hitters),” Gonzalez said. “I mean, really, every other aspect of our game has been pretty solid. We’ve just got to figure out how we can stop the opponent from scoring some runs.”

The clubhouse was quiet, save for the conspicuous raised volume of closer Jason Grilli, who didn’t pitch but complained about questions asked by reporters interviewing Foltynewicz, among other things.

Peterson’s three hits also included a double in a three-run fourth inning. But the leadoff man’s performance — three hits, three RBIs, three runs — was reduced to a footnote after another pitching meltdown.

“We’ve been swinging the bat pretty well as a team,” said Peterson, who has hit .313 in his past 43 games and 368 (21-for-57) with nine extra-base hits and nine RBIs in his past 13 games. “Our guys are putting together good at-bats. I think our (pitching) staff is doing their job of competing and keeping us in there. Every day we’re coming to work, and we know that eventually it’s going to flip.”

Gonzalez also said he’s not run out of hope that the Braves can get their pitching woes worked out, which include not just majors-worst production from the bullpen but also a combined 4.95 ERA with 21 homers allowed in 22 starts from Foltynewicz and opening-day starter Julio Teheran, who has just four wins and a 4.78 ERA.

Cunniff’s ERA is up to 4.68 in 27 appearances, and he’s allowed 15 walks and three homers in 25 innings.

Speaking of the bullpen’s troubles, Gonzalez said, “Well, there’s more things to try. More combinations, other stuff to try. We’ll try to figure it out.”

Foltynewicz left the game with a runner one first and one out in the fifth inning, the Braves still leading 8-5. Cunniff promptly gave up a two-run homer to the first batter he faced, Travis d’Arnaud.

Cunniff walked the next two batters before getting out of the inning with a pair of strikeouts to at least preserve a lead, though it was down to a single run.

Avilan came in to pitch the sixth and allowed a pair of singles to pinch-hitter Michael Cuddyer and Curtis Granderson to start the inning. Juan Lagares then launched a three-run homer to the left-field seats, holding his bat high as he triumphantly left the batter’s box. The Mets had a 10-8 lead, and most in a crowd of 36,340 were thrilled.

Foltynewicz was charged with nine hits including two homers, six runs (five earned) and one walk with three strikeouts in 4 1/3 innings, pushing his ERA to 5.19 in nine starts. He got no decision and has one win and a 5.66 ERA in his past six starts, with 45 hits (including six homers) allowed in 35 innings.

“I just didn’t get the job done,” Foltynewicz said. “I have all the confidence in the world when it comes to the bullpen coming in and saving me. But they are going to have bad days, just like us. The offense came to work today. They give you a five-run lead, you’ve got to take advantage of it. I didn’t do that today. I felt like I let the team down.”