Morales, who lost the title to Marco Antonio Barrera in his last fight, scored repeatedly with right hands against his smaller opponent.

Ayala fought hard until the end and never went down.

But his left eye was swollen shut and he took a beating in the 12th round as Morales pinned him on the ropes and landed punches almost at will.

With just a few seconds left in the final round it looked like referee Kenny Bayless might stop the fight but it went to the final bell for a decision.

Ayala was fighting for the first time at 126 pounds (56.7 kilograms) and although both fighters weighed the same, Morales clearly packed the harder punches.

"He's a very heavy hitter, punches very hard. He also had a reach advantage over me and was catching me at the end of his punches," said Ayala.

Two judges scored it 117-111 for Morales while the third scored it 116-112.

On the undercard, champion Jorge Arce retained the WBC light flyweight title with a third-round technical knockout of Mexican compatriot Augustin Luna.

Welterweight prospect Dmitriy Salita remained unbeaten by stopping an outmatched Ron Gladden midway through the first round of a scheduled four-round fight.

And Mexico's Guty Espadas won a split decision over Clarence "Bones" Adams, who was bloodied by a head butt midway through the fight.

Espadas landed the cleaner punches to win on two of the three scorecards in the featherweight fight.