On the undercard, Thurman (22-0) stunned Soto Karass (28-9-3) with a left hook to the chin that had the Mexican fighter out on his feet. Defenseless, Soto Karass took four more heavy blows before the referee stopped the bout.
Soto Karass caught Thurman with an overhand right to the chin in the opening minute of the bout, staggering the Clearwater, Fla., fighter. Soto Karass followed it with another crushing right, but Thurman withstood the flurry and delivered his own staggering shots to the body and head to close the round.
“He made me bring it out from round one,” Thurman said. “He was ready Round 1. I was dilly dallying in Round 1 and he turned the lights on and woke me up.”
Earlier, Leo Santa Cruz (26-0-1) successfully defended his WBC super bantamweight championship, unanimously outpointing Cesar Seda. The judges scored the bout 116-111, 115-112, 117-110 for Santa Cruz, who landed 43 percent of his power punches in handing Seda his second loss in 27 fights.
Also, Beibut Shumenov stopped Tomas Kovacs in the third round to retain his WBA super light-heavyweight championship. Shumenov, from Kazakhstan, improved to 14-1. Kovacs, from Slovakia, dropped to 23-1.