CARSON, Calif. -- Keith Thurman had an unenviable act to follow when Lucas Matthysse and John Molina Jr. put on a bloody 11-round slugfest right before he stepped in the same ring with Julio Diaz.
Although Thurman couldn't match Matthysse's pyrotechnics, the rising welterweight still managed a big finish.
Thurman remained unbeaten Saturday night, stopping Diaz after three rounds when Diaz's corner threw in the towel due to an injured rib.
Thurman (23-0, 21 KOs), nicknamed "One-Time" for his one-punch knockout power, retained his WBA interim welterweight title. He floored Diaz in the second round before delivering the body shot that led Diaz to quit on his stool on a chilly night before the usual energized crowd at the outdoor ring south of Los Angeles.
Although he had a short night, Thurman still demonstrated his formidable skill and power in his seventh fight in less than two years.
"He's a warrior, but he just couldn't take the punishment," Thurman said about Diaz. "No one knows the power of One-Time until they step in the ring with One-Time. We did the work in the gym. How did you think I was able to look this good?"
A left to the temple dropped Diaz, although he stayed on his unsteady feet for a moment before taking a knee and getting up to beat the count. Thurman remembered the punch that evidently injured Diaz's rib, but thought Diaz (40-10-1) had partially blocked it.
"We were able to put that pain and that hurt on him like we're supposed to," Thurman said.
The main event was an anticlimax after a tenacious performance by Matthysse (35-3, 33 KOs), who overcame two early knockdowns and stopped Molina early in the 11th round of the Argentine 140-pound star's dynamite return to the ring. Matthysse knocked down the bleeding Molina in each of the final three rounds, culminating in a decisive combination.
Matthysse hadn't fought since injuring his eye and losing a decision to 140-pound champion Danny Garcia last September, but he was right back in destructive form.
"It did take me a few rounds to get going, but I was able to take control of the fight," Matthysse said. "The knockdowns threw me off a little, but I was able to get my punches in."
That defeat interrupted the rapid rise of the hard-punching Argentine known as "The Machine," and he returned with what many expected to be a simple fight against Molina (27-4), a Los Angeles-area fighter who infamously got knocked out in the first round of a title shot in 2012.
But Molina showed he was no pushover from the opening round, knocking back Matthysse with a big right hand. Another chopping right out of a clinch in the second round sent Matthysse to his knees on just his second career knockdown.
Although Matthysse controlled long stretches of the bout with his jab and power, he went down again late in the fifth after winning much of the round, dropping to his knees on a punch to the top of his head. Matthysse immediately indicated the punch was illegal in the back of his head, but referee Pat Russell ruled it a knockdown.
"I thought I was going to get him out of there early, but he got it together," Molina said. "There's a reason he's the No. 1 guy in the division. I took his shot all the way through, and I didn't feel it until the end."
Despite a cut near his left eye, Matthysse kept using his jab and power against Molina, who had a large cut on the left side of his head. Matthysse then knocked down Molina late in the eighth round with a left hand and a possible push before punishing him throughout the ninth.
Matthysse dropped Molina again in the 10th round with a combination on the ropes. Molina crumpled into the corner on a relentless barrage of punches early in the 11th, and Matthysse leaped on the ropes to celebrate.
Omar Figueroa Jr. (23-0-1) also retained his WBC lightweight title with a dull split-decision victory over Jerry Belmontes.
U.S. Olympians Joseph Diaz Jr. and Terrell Gausha both remained unbeaten on the undercard.