Brandon Rios barely remained unbeaten with a split-decision victory over Richard Abril on Saturday night after failing to make weight for the lightweight bout.
Juan Manuel Marquez also won the WBO interim 140-pound title with a unanimous decision over Sergey Fedchenko in Mexico City on the split-site pay-per-view card.
Rios (30-0-1, 22 KOs) seemed sluggish and wooden for long stretches of his bout after the former lightweight champion came in two pounds over the 135-pound limit Friday.
The decision appeared to upset many fans at the Mandalay Bay Events Center. Although Abril (17-3-1) fights in an unattractive style, he appeared to control several rounds with superior precision and strategic clinches.
Judge Jerry Roth scored the fight 116-112 for Rios, and Glenn Trowbridge favoured Rios 115-113. Adalaide Byrd scored it 117-111 for Abril.
The mercurial Rios, a rising star in the Top Rank stable of fighters, lost his shot at a $50,000 winner's bonus and the chance to reclaim his title when he failed to make weight in his second straight fight. Rios also lost his belt on the scales last December, missing weight in New York before stopping Britain's John Murray.
Abril, a Cuban who fights out of Miami, was a replacement opponent for Rios after fellow Cuban Yuriorkis Gamboa dropped out of the matchup last month in a contract dispute, turning down what promoters said was a seven-figure payday. Abril won the interim WBA belt last October by beating Miguel Acosta, but this decision ended his five-fight winning streak.
Abril seemed more proficient from the opening bell, peppering Rios with shots and combinations. Rios became more physical in the later rounds, butting his way inside Abril's defence with his head, but Abril frequently wrapped up and minimized the damage.
Rios' left eye became puffy in the late rounds, and he kept forcing his way inside with little result. Both corners raised their fighters in the air after the bout.
On the undercard in Las Vegas, Mike Alvarado remained unbeaten and in line for a 140-pound title shot with a tidy unanimous decision over Mauricio Herrera.
Rios intended to move up to 140 pounds in his next bout, and was hoping for a shot at Marquez this summer at Cowboys Stadium. His weight failures and a lacklustre victory could affect those plans.
Marquez (54-6-1) had little trouble picking apart Fedchenko (30-2) in his first fight since losing a majority decision to Manny Pacquiao in November. Two judges saw the fight 118-110 for Marquez, with a third favouring the multidivision champion 119-109.
Marquez, who still holds out hope for a fourth fight with Pacquiao, hasn't lost to anyone but Pacquiao or Floyd Mayweather Jr. in six years.