Gervonta Davis successfully defended his WBA super featherweight belt with a brutal first round knockout of Hugo Ruiz.

Davis (21-0, 20 KOs) retained his title and stayed unbeaten thanks to his knockout at the 2:59 minute mark of the opening round in Carson, California on Saturday.

Ruiz was a late replacement for former three-division world champion Abner Mares, who withdrew due to a detached retina in his right eye sustained during a training session.

And the Mexican veteran Ruiz (39-4, 33 KOs), a former world champion in lower weight classes, was out of his depth at Dignity Health Sports Park, where the 32-year-old was put to the sword.

Davis barely raised a sweat as he landed a big right hook that cracked Ruiz's nose and left him on his knee.

Ruiz managed to get to his feet, but with blood flowing form his nose, the referee decided to wave off the bout in favour of the 24-year-old champion.

After the fight, Ruiz admitted that Davis was too big and too strong. The contest was Ruiz's first at 130-pounds.

The bulk of Ruiz's career had been fought at 122 and 118-pounds. He only recently moved up to featherweight and had one bout at 126.

"As soon as I felt the first punch. It was everything, the power, his size, the weight, it was too much," Ruiz told BoxingScene.com.

 "As soon as he started landing punches, I could feel them. I have a lot of first round knock outs, today was my turn to lose in the first round. It happens in boxing.”