LAS VEGAS (AP) _ Derrick Gainer's fight plan against Diego Corrales was perfect for two rounds. It turned out he shouldn't have changed it for the third.

Gainer made the mistake of going inside in the third round against the IBF junior lightweight champion Saturday night, and it cost him his bid for the 130-pound title.

The fight was one of two 130-pound title fights at the MGM Grand hotel-casino. In the second fight, WBC champion Floyd Mayweather defended his title against Goyo Vargas.

Corrales knocked Gainer down with a left hook midway through the third round, then put him on the canvas for a second time with a flurry of punches against the ropes seconds later.

Gainer got up at the count of nine, but referee Jay Nady waved the fight to a close at 1:50 of the third round.

``I waited for him to come inside and he did,'' Corrales said. ``I wanted him to fight on the inside. I knew he couldn't take the inside pressure.''

Gainer, who had won 16 straight fights, looked good early, circling the taller Corrales and landing the bigger shots while staying away on the outside.

He changed his fight strategy in the third round, though, coming out and fighting inside against Corrales in the middle of the ring. A left hook suddenly put him down, and Gainer was clearly hurt even though he protested when the fight was stopped.

``I was more hurt after the first time I went down,'' said Gainer, who was the IBF's No. 1 contender.

``I was surprised he went down,'' Corrales said.

It was the second defense of the junior lightweight title for Corrales, who upped his record to 31-0 with 25 knockouts. Gainer, of Pensacola, Fla., fell to 33-5.

Both fighters weighed 130 pounds.

``He was slower than I thought but he hit me with a really good hook in the first round,'' said Corrales, of Sacramento, Calif.