OAKLAND >> Brent Rooker’s two-run walk-off homer might have only been the second coolest thing he did on Monday night.

After the A’s 6-4 win over the Kansas City Royals, the A’s All-Star designated hitter made the short walk over to the Oakland Arena to see country music star Zach Bryan perform in concert. But not only did Rooker see the show, he joined Bryan on stage — wearing his Kelly green A’s jersey — and began to sing alongside the 2022 Grammy Award nominee.

“I don’t even know what happened,” Rooker wrote in an Instagram story late Monday night. “@zachlanebryan is the absolute man. Burned the house down as always.”

Bryan also acknowledged Rooker’s dual talents on Instagram, saying, “Man belted a homer then came and BELTED WITH US.”

Bryan is on his 28-city cross-country “Burn, Burn, Burn” tour that began in May and concludes Aug. 30 in Kansas City, Missouri.

There may have been more people at the concert than at the game. The A’s won in front of their fifth-smallest crowd of the season (3,095) and avoided falling 56 games under .500 for the first time since 1920.

The A’s should have won the game before it got to Rooker’s heroics.

The A’s led most of the game, but squandered a 4-2 lead in the eighth when the Royals scored twice off Lucas Erceg, tying the game.Kansas City had another runner in scoring position when Michael Massey singled and appeared to steal second with two outs. Massey was initially ruled safe, but the call was overturned after a video replay, ending the inning.

Ryan Noda led off the ninth and was hit by a pitch from Royals pitcher Dylan Coleman. Rooker then slammed a 2-0 slider into the seats in left field for his second game-ending homer of the season.

With the concert going on, Rooker, hitting .364 (8-for-22) with three extra-base hits in his previous six games before Monday, made sure the game with the Royals didn’t last any longer than it had to with his 21st homer of the season. The game ended at 9:28 p.m., likely after Bryan’s show had started.

“Rook’s been swinging the bat pretty well of late,” A’s manager Mark Kotsay said. “I know he really wanted to get to this concert next door ... so he took it into his own hands.

“It’s a good feeling to win tonight after we coughed up a 4-2 lead. I would have hated to be on the other end of that.”

Rooker’s homer meant the MLB-worst Athletics (35-90) snapped a three-game skid and won for the second time in 10 games.

“It’s exciting,” Rooker told NBC Sports California. “Just trying to get something in the middle of the plate there at 2-0. Put a good swing on it .. and it had enough to get out here.”