ATLANTA — For most of the afternoon and then following an Edwin Diaz implosion it appeared “OMG” — one more game — would be needed for the Mets.

Francisco Lindor took those three letters to another meaning with one swing in the ninth inning Monday that thrust the Mets into the postseason with an 8-7 victory over the Braves in the first game of a doubleheader at Truist Park.

Lindor’s two-run homer gave the Mets the runs they needed for their 89th victory — their magic number as the day began for a National League wild-card berth.

The Mets will open the best-of-three NL Wild Card Series on Tuesday against the Brewers in Milwaukee. The Braves won 3-0 in the nightcap of the doubleheader to claim the other remaining wild-card berth and will face the Padres.

In an epic finish, the Mets rallied from a 3-0 deficit with six runs in the eighth and then watched Diaz flush the lead before Lindor hit one of the biggest home runs in franchise history for the lead. Diaz then got the final three outs.

“Pretty wild,” Lindor said of the emotional swing. “It felt like the whole week the emotions have gone like that. It was a great ballgame. They gave everything they had and we did as well. It was just a pitch here and there. I think that is the way the game was won today. It was just one more pitch than the other team.”

Team owner Steve Cohen was there to greet his players on the top step of the dugout following the final out.

“I have never seen anything like it — it was a roller coaster,” Cohen said. “I was in tears in the eighth inning when we went ahead. I was in shock when we lost the lead and then Francisco stepping up, an incredible moment.”

Diaz insisted to manager Carlos Mendoza he return to the mound for the ninth after his hellacious eighth inning (he had entered for a five-out save behind ineffective Phil Maton and allowed two earned runs on three hits and a walk).

After recording the final out with the tying run at second base, Diaz spiked his glove to begin the celebration.

“I was feeling a little bit tired, but I have got to fight,” said Diaz, who threw 40 pitches. “This team gave me so much and they trusted me. I didn’t want to be the guy who screwed up. I want to fight for this team, for these guys … when I saw Lindor hit the homer, I said, ‘I have to go out and fight for the team.’ ”

In the eighth, Diaz unraveled with his control and didn’t cover first base on Jarred Kelenic’s grounder to Pete Alonso, allowing Kelenic to reach. Ozzie Albies’ three-run double gave the Braves a 7-6 lead.

Spencer Schwellenbach frustrated the Mets with seven superb innings — he was charged for one earned run — but after the right-hander was removed the party began.

The climax was Brandon Nimmo’s two-run blast against Raisel Iglesias that extended the Mets lead to 6-4 after Mark Vientos’ sacrifice fly put them up, 4-3.

Francisco Alvarez had an RBI double in the inning and Lindor contributed an RBI single. Jose Iglesias tied it with an RBI single.

“It’s been an uphill fight,” Lindor said, referring to a season in which the Mets at their nadir in May were 11 games below .500. “We put ourselves in a big hole and we kept climbing. We kept our shoulders above water after the All-Star break. We never believed that we were drowning.”

Tylor Megill kept the Mets in the game by allowing three earned runs over 5 ²/₃ innings. The right-hander surrendered eight hits and walked two, but also struck out eight. He was making his first start since Sept. 22.

Albies delivered a two-run homer in the third that put the Mets in a 2-0 hole. Megill allowed a leadoff single to Michael Harris II before Albies connected on a slider and cleared the left-field fence.

Megill had to work to get through the inning, after Matt Olson and Ramon Laureano each singled and got to second and third on Alvarez’s passed ball. But Megill struck out Travis d’Arnaud to escape.

Laureano’s homer in the sixth widened the Met deficit to 3-0. It came after two straight innings in which Megill had faced the minimum number of batters.

Megill was removed after allowing a two-out single to Gio Urshela in the sixth. Huascar Brazoban entered and walked Orlando Arcia before recording the final out.

“It was one of the craziest games I have ever been a part of,” manager Carlos Mendoza said.