LAS VEGAS -- Faced with his stiffest competition yet, Devin Haney came of age with the best performance of his career.

Haney, 23, retained his WBC lightweight title with a unanimous-decision victory over Joseph Diaz Jr. on Saturday at MGM Grand Garden Arena, but the challenger made him earn it following a slow start.

One judge scored the fight 116-112, while the two other judges each scored it 117-111. Haney jumped out to a commanding lead on the strength of a sharp jab, clean punching and surprising activity.

But even when Diaz finally fought his way into the bout in Round 4, Haney was ready and willing to exchange on the inside. Diaz found a home for his overhand left during the remainder of the bout, but particularly in Rounds 9 and 12. Plenty of those sweeping lefts landed flush, but Haney never wavered.

Instead, he always returned fire and connected with stinging straight right hands and uppercuts that scored.

"He said he was going to bring the dog out of me and that's exactly what he did," said Haney, a Las Vegas resident. "He hit me with some good shots. They say I have no chin, but I think I showed it in this fight."