HOUSTON -- Juan Manuel Marquez took care of Juan Diaz.
Now he wants Floyd Mayweather Jr.
Marquez (50-4-1, 37 KOs) won the vacant WBA and WBO lightweight belts, plus Diaz's minor IBO title, by knocking out the Houston native with a right uppercut at 2:40 of the ninth round Saturday night.
The 35-year-old Marquez, a former featherweight and super-featherweight champion, was fighting at 135 pounds for only the second time in his professional career.
Moments after the victory, Marquez said he didn't want to stay in the lightweight division for long and wanted to challenge Mayweather, who was considered the pound-for-pound king when he retired last summer.
The unbeaten five-division champion said he no longer had the desire to fight, but every major contender anywhere near the welterweight division has been a rumored opponent for him.
And now Marquez thinks he's earned a shot.
"Who wouldn't want to see that fight?" Marquez said through an interpreter. "I'll fight him at 140, maybe a little above that. I want to fight the best, the very best."
Marquez has been trying for months to land one more fight with Manny Pacquiao, who will face Ricky Hatton on May 2. Marquez fought Pacquiao to a draw in May 2004, then lost a close decision in the rematch last March.
But Marquez says he's given up on Pacquiao, and now wants to focus on luring Mayweather out of retirement.
"I've been trying to get a third fight with Manny Pacquiao, but he doesn't want to fight me," Marquez said. "So I'm calling out the best, and that's Floyd Mayweather."
Marquez and Diaz both fight for Oscar De La Hoya's Golden Boy Promotions. De La Hoya backed Marquez's challenge, and believes Mayweather will fight again.
"Marquez wants to go for the best," De La Hoya said. "That's the fight he wants. We feel that, with Marquez, he is always going for that pound-for-pound title. If Mayweather comes back, then he would be fighting the best pound-for-pound fighter in the world in Mayweather."
Diaz (34-2), meanwhile, collapsed in what he called the most important fight of his life. His other defeat was to Nate Campbell, whose WBA and WBO titles were stripped after he failed to make weight for his own defense two weeks ago.
Marquez opened a cut over Diaz's eye in the eighth round, then knocked him down twice in the ninth. He landed a hard right in the middle of the ring, the first of a four-punch combination that dropped the 25-year-old in his tracks.
Referee Rafael Ramos allowed the fight to continue, and Marquez moved in and connected with another right uppercut. When Diaz went down, Marquez ran to his corner and hopped onto the ropes, exhorting the thousands of Mexican fans in attendance.
"I was ready to leave my heart and my soul in that ring," Marquez said. "It was a great victory for me. It is one of the most important victories of my career."
Diaz won the early rounds, repeatedly backing Marquez into the ropes before hammering him with quick combinations. He snapped back Marquez's head with a hard left in the third, but Marquez fought out of the corner and connected with a right uppercut in the middle of the ring.
Diaz continued to force Marquez into the ropes and the Mexican fighter was constantly trying to punch out of trouble.
Marquez turned the momentum when he cut Diaz in the eighth, a similar situation to Diaz's bout against Campbell, when a cut seemed to change the entire fight.
Diaz acknowledged that the cut bothered him.
"I got caught with a good punch. There was nothing I could do," he said. "I couldn't see out of my right eye."
Headlining the undercard, Chris John retained his WBA featherweight title by battling hometown hero Rocky Juarez to an entertaining draw.
An Indonesian making his North American debut, John (42-0-2) successfully defended his belt for the 11th time. He wanted to put on a good show in Houston to catapult himself into more fights -- and bigger paydays -- in the United States, and certainly didn't hurt his chances.
John seemed to take control of the fight in the middle rounds, but Juarez rallied to take the final two. All three judges scored the fight 114-114.
Juarez (28-4-1) failed to win a title fight for the fifth time. He lost to Marquez -- who, incidentally, lost to John almost exactly three years ago -- for the featherweight title in November 2007, then knocked out Jorge Barrios last September to set up another title shot.
Both fighters claimed victory afterward, and De La Hoya said he'd like set up an immediate rematch. John certainly seemed less bruised in the post-fight news conference. Juarez wore sunglasses to hide two swollen eyes.
"Look at my face -- it's all right," John said with a smile. "Look at my opponent's face. You can judge."