Juan Manuel Marquez makes his case with unanimous decision over Juan Diaz

Reporting from Las Vegas — 

He has taken almost to begging, but Juan Manuel Marquez no longer needed to throw out the hyped-up empty words that too often scar his sport.

Saturday night at Mandalay Bay Events Center, Marquez’s case to fight Manny Pacquiao for a third time was delivered in a relentless display of brutal toughness as he brilliantly dismantled a man 10 years his junior, beating Juan Diaz by unanimous decision to retain two world lightweight belts.

Marquez (51-5-1) won by scores of 118-110 from judge Glenn Trowbridge, 117-111 from Patricia Morse Jarman and 116-112 from Jerry Roth to retain his World Boxing Assn. and World Boxing Organization belts in front of a crowd of 8,383.

“The trilogy with Pacquiao is what I want,” said Marquez, who fought the Filipino star to a 2004 draw and lost a split-decision to him in 2008. “It’s what everyone wants to see. It’s good for all the fight fans. The Mexicans, the Filipinos all want to see it. I’ll be ready to fight in November, so hopefully Pacquiao will take the fight.”

Pacquiao isn’t expected to. Blown off by Floyd Mayweather Jr., Pacquiao has already agreed to fight Antonio Margarito on Nov. 13 in a 154-pound bout.

Mexico’s Marquez, 36, who beat Diaz (35-4) by ninth-round knockout last year in a bout voted fight of the year by the Boxing Writers Assn. of America, met Diaz’s charging style head on, landing hard jabs and rights that slowed the younger man’s attempts. He outlanded Diaz in all 12 rounds, connecting on 288 punches to Diaz’s 155.

“I fought the best fight I could,” Diaz said. “I didn’t want to stand in front of him. The game plan was to get in there, go in, get off combinations, step around him and get out.”

Diaz’s broken lip showed he wasn’t successful.

“It was hard,” Diaz said. “I got hit with a couple of hard shots. He’s a very tough fighter, a great fighter. I was in there with the best.”

Marquez crushed Diaz with a fourth-round right uppercut, and even as his right eye swelled from some highly entertaining exchanges in the first half of the bout, Marquez remained undeniably willing to stand firm in the face of Diaz’s pursuit, landing a brutal right as the challenger barged ahead in the ninth. Diaz had no choice but to finally back up.

Even if Diaz was able to produce a stirring exchange at the final bell, it was clear who stood as the superior boxer.

“Like every true Mexican warrior, we fought with all our hearts and left it all out there,” Marquez said.

Diaz, studying to take a law school entrance exam, has lost four of his last six fights. “I don’t want to say tonight whether I’ll fight again or not,” he said.

Marquez will fight again, of course. If he can’t get Pacquiao, he could take on 140-pound champion Amir Khan, who was in attendance Saturday, or meet Robert Guerrero.

Guerrero, a Gilroy, Calif., fighter who gave up his world super-featherweight belt to care for his wife, Casey, during her battle against leukemia, returned for his first major fight since her recovery and scored a knockdown and a unanimous decision over former two-division world champion Joel Casamayor in an undercard bout.

Guerrero (27-1) decked Casamayor (37-5-1) in the third round with a short right seconds after hurting the Cuba native with a hard left that backed him to a neutral corner post.

Judges Robert Hoyle and Dick Houck gave Guerrero a 98-89 victory, and Lisa Giampa scored it 97-90 in Guerrero’s favor.

lance.pugmire@latimes.com