LAS VEGAS, FEB. 17 -- Michael Carbajal unleashed a devastating left hook in the second round tonight to score a one-punch knockout of Macario Santos and retain his International Boxing Federation junior flyweight title.

Carbajal's shot put Santos flat on his back, where he stayed as referee Richard Steele counted him out at 1:09 of the second round.

The sudden end to the fight came after Carbajal had scored with a pair of right hands and seemed to be taking control of the scheduled 12-round bout at Caesars Palace.

After the second right, Santos moved to his left and Carbajal shot out a left hook that landed solidly on the side of Santos's face.

"I knew it was just a matter of time," Carbajal said. "I was setting him up with my jab to see if I could set up a clean shot."

Carbajal, 108, successfully defended his 108-pound title for the second time, both by knockout. The 1988 Olympic silver medalist has knocked out his last six opponents.

Santos, 107, actually held his own in the first round of the fight, circling and throwing jabs while Carbajal waited patiently for an opening.

The champion began connecting with the right hand in the second round, however, and the end came soon after.

It was the first fight outside of Mexico for Santos, the IBF's No. 7 contender, who fell to 27-2-1. Santos, who earned $7,000, was stopped for the first time in his career.

Carbajal, who earned $100,000, improved his record to 19-0 with 13 knockouts.

Carbajal, 23, won the IBF title last July with a knockout of Maungchai Kittikasen. Sunday's title fight was the first for the Phoenix native outside the area of his hometown.

In another bout, Scotty Olson, who lost to Carbajal in the 1988 Olympics, remained undefeated by stopping Martin Llovera of El Paso, Texas at 2:31 of the second round.

Olson, 111, improved to 12-0 with 10 knockouts.