Former Giants defensive end Matt Mitrione isn’t doing too badly in his second career.

Mitrione scored a stunning first-round knockout of Russian heavyweight legend Fedor Emelianenko on Saturday night before a packed crowd at BellatorNYC at Madison Square Garden.

Mitrione (12-5) and Emelianenko (36-5) went to the canvas early in the first round when they landed simultaneous right hands. Mitrione was the fastest to his feet after the double knockdown and began landing a series of punches that rendered Emelianenko defenseless. The referee stopped the bout just 1:14 into the round.

Mitrione, who played for the Giants in 2002, put on his No. 98 Giants jersey in the cage after his victory.

“I didn’t know we both dropped,” Mitrione said. “I looked up and said, ‘I have to jump on him.’ ”

Mitrione finished Emelianenko, who was making his Bellator debut. “We all love Fedor,” Mitrione said. “Let’s hope he makes it back.”

In other fights, Heather Hardy needed seven stitches to close a gash over her swollen left eye. But the damage wasn’t about to damper her mood after winning her MMA debut.

Hardy, 20-0-1 as a women’s professional boxer, earned a TKO with just second remaining in round three over Alice Yauger as part of the BellatorNYC prelims televised on Spike TV.

“I’m so happy right now I don’t care I have stitches on my face,” Hardy said. “I hope I proved to all those people that thought I was just doing it for attention that I can really fight.”

On the pay-per-view card, Chael Sonnen won a unanimous decision over Wanderlei Silva at light heavyweight in the main event. Douglas Lima successfully defended his welterweight title with a unanimous decision over Lorenz Larkin.

Zach Freeman submitted Aaron Pico, a highly touted prospect making his pro debut, in the first round, and Brent Primus won the lightweight title when defending champ Michael Chandler couldn’t continue after injuring his ankle in the first round.

In the main event of the prelims, Ryan Bader (23-5) defeated Phil Davis by split decision in his Bellator debut to win the light heavyweight championship.