Mexico’s Oscar Valdez retained his WBC super-featherweight title with a unanimous points victory over Brazil’s Robson Conceicao.
Valdez, 30, had been cleared to fight despite failing a drug test.
Judges at Casino del Sol in Tucson, Arizona, awarded the fight to Valdez 117-110, 115-112, 115-112.
On the undercard, Japan’s Junto Nakatani retained his WBO flyweight crown with a fourth-round knockout of Puerto Rican challenger Angel Acosta.
Former Olympic champion Conceicao, 32, took the fight to the man he had beaten as an amateur and started the stronger.
But as he tired, Valdez started to take the upper hand and judges decided he had done enough to win.
Some have questioned whether the fight should have gone ahead at all after Valdez failed a test for the banned substance phentermine, a weight-loss drug, but was cleared to fight by a gaming commission.
Valdez insisted he was a clean fighter and believed he had accidentally ingested it via a herbal tea, while WBC president Mauricio Sulaiman said phentermine was not a performance enhancer.
Before the main bout, Nakatani extended his unbeaten record to 22-0 after stopping Acosta. It was a first title defence for the 23-year-old Japanese, and the first time he had fought outside his own country.
