LAS VEGAS – Steven Nelson knew he would encounter a fighter Saturday who was better than his record indicated.

Raiko Santana showed him almost immediately that he is much better than even Nelson realized. The Cuban-born Santana stunned Nelson by stopping him in the first round of their 10-round light heavyweight fight on the Canelo Alvarez-Terence Crawford undercard at Allegiant Stadium.

Santana nailed Nelson with a right hand that knocked him into the ropes with just over 30 seconds to go in the opening round. He realized Nelson was hurt and unloaded a barrage of power punches that made Nelson stumble backward and caused referee Robert Hoyle to stop their fight 2:38 into it.

Nelson never went down, but Hoyle determined he was too hurt to continue. Nelson, who lost by knockout or TKO for the first time as a pro, seemed stunned that their fight was stopped.

Nelson (20-2, 16 KOs) entered the ring as an approximate 3-1 favorite over Santana (13-4, 7 KOs), according to most sportsbooks, but Santana seized the opportunity of his lifetime on this highly publicized undercard.

“This is the win that was missing for me,” Santana told The Ring’s Max Kellerman following his huge win. “I think I’m in a great moment in my career. I wanted to show my work and, as you saw, [that was] the result.”

The 37-year-old Nelson, one of Crawford’s closest friends, had hoped to bounce back from his first professional loss 7½ months ago by beating a skillful Cuban veteran who upset Joseph George (then 12-0) and Lorenzo Simpson (then 14-1) on points in two of his four previous fights.

Nelson lost his previous bout to Diego Pacheco by unanimous decision Jan. 25 at The Cosmopolitan of Las Vegas. Pacheco (24-0, 18 KOs), who is ranked No. 3 among The Ring’s super middleweight contenders, beat Nelson by the same score, 117-111, on all three scorecards.