Juan Manuel Marquez stamped himself as the world's top lightweight with a ninth-round knockout of Juan Diaz in a thrilling title unification fight Saturday night at the Toyota Center.

Marquez (50-4-1, 37 KOs) won the vacant WBA and WBO lightweight belts, plus Diaz's minor IBO title, finishing off the Houston native with a right uppercut at 2:40 of the ninth round. The 35-year-old Marquez, a former featherweight and super-featherweight champion, was fighting at 135 pounds for only the second time in his 15-year professional career.

Diaz (34-2) called the fight the most important of his life, but he lost for the second time in three fights. 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.

Moments later, Marquez boastfully called out retired pound-for-pound king Floyd Mayweather Jr.

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. Marquez pounded him in the middle of the ring with uppercuts late in the round, and blood was gushing down the side of Diaz's face when the bell sounded.

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 his 11th time. He wanted to put on a good show in Houston to catapult himself to 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.

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