Dmitry Pirog puts away Daniel Jacobs

LAS VEGAS -- Daniel Jacobs' dream of winning a world title came crashing down at the end of a big right hand from Dmitry Pirog.

Russia's Pirog, unheralded, unknown in the United States and a 3-1 underdog, landed a huge overhand right hand in the fifth round, knocking Jacobs flat on his back to win a vacant middleweight title Saturday night at the Mandalay Bay Events Center in the final bout before the Juan Manuel Marquez-Juan Diaz lightweight championship rematch in the main event.

Jacobs (20-1, 17 KOs), 23, was the 2009 ESPN.com prospect of the year and had been dominant so far in his career, albeit against limited opposition. But Pirog (17-0, 14 KOs) was not very experienced either against top competition, although the knockout was highlight-reel material. It netted him a belt that lineal champion Sergio Martinez had been stripped of in May.

Pirog, 30, flashed the right hand in the second round, nailing Jacobs with it and knocking him into the ropes. But through the first four rounds Jacobs led on 39-37 on all three scorecards until Pirog, who was making his American debut, ended the fight.

Jacobs, 23, went down and didn't move, causing referee Robert Byrd to waive the fight off at 57 seconds without finishing his count. When Byrd waived it off, Jacobs tried to protest, but it was too late.

"After the second round, I knew I was good. I hurt him in the second and I knew I could come back and do it again," Pirog said. "I'm very happy and thankful to take this belt back to my fans in Russia. Danny was a dangerous fighter and punched quickly and sharply. So I had to be cautious, but I didn't feel much from him."

The loss was just the latest disappointment for Jacobs, who was fighting just a week after his grandmother, Cordelia Jacobs, who helped raise him, died of lung cancer. He dedicated the fight to her and was scheduled to be home for Sunday's funeral.

"I'm not going to complain, I just hope everyone will forgive me and keep the faith," Jacobs said. "I know I can come back and become a champ. I think if I was 100 percent, I would have done better, but this is one of those things that happen. Everything happened so fast. I got caught with a shot I didn't even see. I'll be OK."

Guerrero dominates Casamayor

The junior welterweight division is perhaps boxing's hottest and Robert Guerrero made the statement that perhaps he should also be included in the conversation about big fights at 140 pounds.

Guerrero, a former featherweight and junior lightweight titlist with limited experience at lightweight, jumped up to junior welterweight for the first time and routed Joel Casamayor for a unanimous decision, winning 98-89 (twice) and 97-90. ESPN.com also had it for Guerrero, 98-89.

Casamayor, 39, is a former lightweight and junior lightweight champion one of the craftiest veterans in the sport, but his age apparently has caught up to him.

His legs didn't look steady and he offered very little on offense. Guerrero's punches, especially his straight left hand, wobbled him several times.

It was only Casamayor's second fight since losing the lightweight championship to Marquez via 11th-round knockout in 2008, and he could be headed into another long layoff after the loss and uncertainty about his ring future.

Guerrero (27-1-1, 18 KOs) dropped Casamayor (37-5-1, 22 KOs) in the second round with a short right hand, which came moments after referee Jay Nady deducted a point from Casamayor for holding.

"I had a dominant performance. He's a lefty and he's really crafty with a good counter punch," Guerrero said. "He kept grabbing me and holding me down. He's a veteran and he knows how to survive."

Casamayor made it interesting late in 10th round when he nailed Guerrero with a right hook for a knockdown, the first of Guerrero's career. But Guerrero appeared more embarrassed than hurt as he scrambled to his feet and finished the final minute of the fight.

"I just shook my head and said I got hit with a good punch," Guerrero said. "I took my time and got up. Hopefully, I'll get the winner of the Marquez-Diaz fight."

Said Casamayor, "In the first two or three rounds I was little confused, but I got my rhythm back. Robert is tall, so it was a little awkward to fight him. I think if I landed one more punch in the last round that it would have been over. But I was a little bit rusty. I'll still fight anybody."

Guerrero, 27, dedicated the fight to his wife, Casey, who has been battling leukemia since 2007 but was well enough to make the trip to Las Vegas. She had been in bad shape late last year and early this year, causing Guerrero to pull out of a lightweight title bout and have an eight-month layoff, which he ended in April.

Linares dominates Juarez

Former two-division titlist Jorge Linares (29-1, 18 KOs) laid a beating on Rocky Juarez (28-7-1, 20 KOs) in a lightweight fight, winning a unanimous decision and his second in a row after being knocked out in the first round and losing his junior lightweight title last fall.

In his comeback fight, Linares struggled to a majority decision win against Francisco Lorenzo, but against Juarez, he looked like the same dynamic fighter that made him one of the most highly regarded young fighters in boxing.

Linares, 24, battered Juarez for most of the fight. He knocked him down near the end of the fifth round with a left uppercut and badly swelled both of his eyes with a pinpoint two-handed attack.

Juarez mounted a bit of a rally in final two rounds, clipping Linares with a right hand in the ninth that made him spit out a mouthful of blood and keeping him on the run in the 10th round, but it was too little, too late. The judges gave it to Linares, 99-90 (twice) and 97-92. ESPN.com also had it 97-92 for Linares, the Venezuela native fighting in the United States for only the second time.

Juarez, 30, a 2000 U.S. Olympic silver medalist, probably saw his days in significant fights comes to an end. Juarez, who is 0-5-1 in junior lightweight and featherweight title bouts, fell to 1-4-1 in his last five bouts.

Bika disqualified

Although he was separated from his senses, France's Jean Paul Mendy became the mandatory challenger for a super middleweight world title when Sakio Bika was disqualified for crushing him with a right uppercut while he was down in the first round of their elimination fight.

It ended with Mendy out cold on the canvas but declared the winner.

Bika, the 2007 winner of "The Contender," stormed to Mendy (29-0-1, 16 KOs) in the opening seconds and had him in a corner looking for cover. But after Bika landed a left hook that knocked Mendy to his right knee, he threw a ferocious right hand that hammered Mendy on the jaw. Mendy, who never saw the right hand, keeled over face first and was motionless for several minutes. Referee Joe Cortez had no choice but to disqualify Australia's Bika (28-4-2, 19 KOs) at 1 minute, 19 seconds.

"I'm really disappointed. I was excited and I never saw that his knee was on the canvas," Bika said. "I want to be in the big fights, so this is really disappointing."

Mendy, 36, who was coming off a ninth-round knockout of Josival Lima Teixeira in March, becomes the mandatory challenger for the winner of the Oct. 15 fight between 168-pound titlist Lucian Bute and Jesse Brinkley.

Mendy, who spent several minutes after the fight sitting on a stool with medical personnel hovering over him, was taken to the hospital as a precaution.

Bika, 31, was fighting for the first time in almost exactly a year. He hadn't fought since scoring a first-round knockout of Nestor Casanova in Australia last July 30.

Gomez scores easy KO

Junior welterweight Frankie Gomez (5-0, 5 KOs), Golden Boy's prized 18-year-old prospect from East Los Angeles, blew out Ronald Peterson (2-3, 2 KOs) in 2 minutes, 14 seconds.

Gomez turned pro in April after winning a silver medal in the 2009 world amateur championships and gold in the U.S. nationals.

Gomez rolled past Peterson with ease, putting him away with a right to the chin followed by a left hook that knocked him down. Peterson was squatting with one arm grabbing the ropes while he thought about whether he was going to get up while referee Kenny Bayless counted him out.

• With heavyweight titlist David Haye in his corner helping out trainer Adam Booth, 22-year-old British super middleweight prospect George Groves (10-0, 8 KOs) made his American debut and methodically broke down Mexico's Alfredo Contreras (11-8-1, 5 KOs) for a sixth-round TKO in their scheduled eight-rounder.

Groves peppered Contreras throughout the fight and when referee Russell Mora stepped in at 48 seconds of the sixth it was not because Groves has badly hurt him. The stoppage was more from an accumulation of blows while Groves was not answering.

• Seth Mitchell (18-0-1, 12 KOs), perhaps America's best heavyweight prospect, overwhelmed onetime fringe contender Derek Bryant (20-6-1, 17 KOs), needing just 1 minute, 45 second to take him out.

Mitchell, 28, former Michigan State linebacker from Brandywine, Md., came out fast to attack the 39-year-old Bryant, a southpaw who hadn't fought in nearly two years. Mitchell quickly found a home for his left hook to the body, drilling Bryant with about half dozen of them before moving his attack to the head. He landed several shots and when a right uppercut sent Bryant's head snapping back, referee Kenny Bayless jumped into stop it. After Bryant regained his senses, he complained about the stoppage but it appeared to be on the money.

• Lightweight Juan Manuel Montiel (6-3-1, 1 KO), a Marquez protégé, easily outpointed Mike Peralta (4-6, 1 KO), winning 60-53 and 58-55 (twice).