LAS VEGAS -- Robert Guerrero's nickname is "The Ghost," and Saturday night he was invisible against Orlando Salido.
Heralded since his 2001 pro debut as a potential star, Guerrero turned in a terribly disappointing performance and lost a unanimous decision and his featherweight title to Salido on Saturday night at Mandalay Bay.
The lackluster fight was the co-featured bout on the card headlined by Carlos Baldomir's welterweight title defense against pound-for-pound king Floyd Mayweather Jr., and it did little to stoke the crowd for the main event.
Salido (28-9-2) was an underdog, but he was more experienced than Guerrero, 23, and it showed. He won 118-111, 117-111 and 115-113 on the scorecards. ESPN.com had it 116-112 for Salido.
"It was not an easy fight. It was a very hard fight," Salido said. "I am very happy about winning this championship. I learned a lot from the other championship fight I lost."
It was the second title opportunity for Salido, who challenged then-unified champion Juan Manuel Marquez in September 2004 and lost a lopsided unanimous decision.
Salido, 25, of Mexico, was very effective throughout the fight with his straight hand, of which Guerrero couldn't get out of the way.
In the eighth, Salido, a mandatory challenger, hurt him with a strong left-right combination that buckled Guerrero, who seemed to grow more and more dejected as the fight wore on.
Salido, of Gilroy, Calif., had another big round in the 10th, rocking Guerrero (19-2-1), who had little response.
Many figured the fight would be easy for Guerrero, who was coming back quickly after winning his title on Sept. 2, when he easily dismantled Eric Aiken for an eighth-round TKO.
But two months and two days later, his title is gone. It is the fourth consecutive time that the IBF featherweight belt has changed hands since the politically motivated stripping of Marquez.
Welterweight contender Paul Williams (32-0, 24 KOs) easily defeated late substitute Santos Pakau (27-4-1) in a showcase fight, stopping him at 2:16 of the sixth round.
Williams, 25, is awaiting a mandatory shot against titlist Antonio Margarito, who faces Joshua Clottey on Dec. 2, but he'll fight whichever champion will give him an opportunity.
"I'm ready to fight for a championship at 147 [pounds]," Williams said. "I'll take the winner of Mayweather-Baldomir or whoever else. I'm on a belt-collecting mission."
The 6-foor-1 Williams towered over Pakau and dominated the fight. He dropped Pakau to a knee with a combination in the first round, knocked him down again in the second, and gave him a bloody nose in the third.
Although Pakau showed enormous heart and landed a good shot in the fifth, Williams spent the last 30 seconds of the round relentlessly pounding him along the ropes.
Finally, in the sixth, with Williams continuing to dish out tremendous punishment, referee Joe Cortez stopped the fight, although there was no particularly crushing blow that led to the stoppage.
Williams, a southpaw with a build reminiscent of Thomas Hearns, was originally supposed to face journeyman Mauro Lucero in a 10-rounder, but Lucero was beset by problems getting into the United States from Mexico, and when he finally arrived Friday night, he was dramatically overweight.
But organizers had known of his problems and had Pakau on standby ready to fill in, which he did in a fight reduced from a scheduled 10-rounder to an eight-rounder.
• Heavyweight Chris Arreola (18-0, 16 KOs) slowly but surely took over the fight with Damian Wills (21-1-1) to score a TKO at 2:17 of the seventh round.
It's unusual for unestablished, undefeated heavyweight prospects to face each other, but they took the gamble, and it paid off for Arreola.
Wills, who is co-managed by actor Denzel Washington, opened a cut over Arreola's right eye in the first round, but that was seemingly where his good fortune ended.
Arreola responded with a huge second round, battering Wills around the ring. Referee Kenny Bayless looked like he was close to stopping it, but Wills was throwing back just enough to keep the fight going.
Although the action slowed, Arreola, 25, continued to pepper Wills, 26, with punches as the rounds wore on until finally backing him into a corner and landing a sustained flurry that forced Bayless to stop the fight.
• On Friday, a 10-round lightweight fight between former junior lightweight titlist Robbie Peden (25-3, 14 KOs) of Australia and Mayweather-managed Wes Ferguson (14-1-1, 3 KOs) was canceled. The fight, which was not going to be part of the televised card, was called off because Peden was overweight. While Ferguson was at the contract weight of 136, Peden was 141½ pounds. He refused to drop the weight, saying he was already too drained, and Ferguson opted to pass on the fight.
Dan Rafael is the boxing writer for ESPN.com.