ATLANTA — The Mets regained a potent weapon against lefties on Wednesday when Wilmer Flores was activated from the 10-day disabled list. His return came just in time to face Braves southpaw Jaime Garcia in Thursday’s series finale.

Flores had been on the DL since April 21, sidelined by a staph infection in his right knee that had doctors initially considering surgery. He spent four days in a New York hospital instead, dodging the operating table because he showed improvement with antibiotics.

“It was scary,” said Flores, who still doesn’t know what caused the infection.

The issue began as a small bump on his right knee that he likened to a mosquito bite. He played one game through the swelling, which only got worse. Pain eventually radiated from his hip down to his knee, a signal that something was wrong.

Flores’ return came a day after manager Terry Collins said that he expected the infielder to meet the team in New York on Friday for the beginning of a series with the Marlins. But when catcher Travis d’Arnaud reaggravated his bruised right wrist during Tuesday’s game, leaving his status for Wednesday up in the air, the Mets needed an extra bat.

Red faced

advertisement | advertise on newsday

Reliever Addison Reed said he was upset at himself — not Collins — when cameras spotted him having a heated exchange with the manager in Wednesday’s 16-5 win over the Braves. “I think I caught some people off guard,” Reed said, after pitching in the seventh, an inning earlier than he ordinarily would appear.

Collins said he wanted to explain to Reed the rationale of the move. He wanted the setup man facing the middle of the Braves lineup, which Reed said was not an issue.

Extra bases

D’Arnaud did not appear in the game . . . Lefthander Sean Gilmartin was sent to Triple-A Las Vegas to make room for Flores . . . The Mets will promote Rafael Montero from Triple-A Las Vegas to start on Friday in place of the injured Noah Syndergaard.