Showtime Presents: Castillo-Diaz/ Lacy-Williams.

A pair of potentially explosive match-ups will be shown during SHOWTIME’s Free Preview Weekend when two-time time World Boxing Council (WBC) Champion Jose Luis Castillo takes on former International Boxing Federation (IBF) titleholder Julio Diaz and undefeated Jeff Lacy risks his IBF super middleweight crown against once-beaten Rubin Williams on SHOWTIME CHAMPIONSHIP BOXING Saturday, March 5. The world championship doubleheader, which will be co-promoted by Top-Rank, Inc., and Gary Shaw Productions, LLC, will take place at Mandalay Bay Resort & Casino in Las Vegas and start at 10:30 p.m. ET/PT (delayed on the west coast). Immediately preceding the scheduled 12-round world title fights on March 5 will be ONE NIGHT, ONE STAR, USHER LIVE. The multi-award-winning recording artist and superstar, Usher will burn up the stage with the concert event of the year from San Juan’s Coliseo de Puerto Rico. From Friday, March 4, through Monday, March 7, SHOWTIME will offer a free preview weekend for viewers nationwide.

Castillo (51-6-1, 45 KOs), of Sonora, Mexico, thought his second defense during his second stint as WBC lightweight champion would be against Diego “Chico’’ Corrales. However, a fight with the World Boxing Organization (WBO) 135-titleholder could not be finalized, so now he is facing Diaz, who has been calling him out for years.

“Even before I won a world title, fans knew what to expect when I fought and that was 100 percent effort,” Castillo said. “I came late into the championship so there is no way I can give anything less. I definitely want to take advantage of my opportunities and put on a good show.

“There is no way I will let down against Diaz or underestimate him. I know he is a very good fighter. He has wanted to fight me since I was champion the first time. I expect him to give 100 percent – just like me. This is going to be a very good fight.’’

A protege of Julio Cesar Chavez, Castillo rallied to retain his belt with a 12-round split decision over former 130-pound world champion Joel Casamayor Dec. 4, 2004, on SHOWTIME from Mandalay Bay. In a classic puncher versus boxer match-up that had fans on their feet during the final nine minutes, Castillo took the last three rounds on all three judges’ scorecards to triumph by the scores of 117-111, 116-112 and 113-115.

“I knew I had to do it in the late rounds because I could not figure him out until the seventh,” Castillo said. “From the beginning, I thought the winner was the going to be the one who had the most heart and courage. I proved that at the end of the fight. It was all about heart.’’

Castillo, who won the WBC 135-pound belt the first time with a 12-round majority decision over Steve Johnston on June 17, 2000, regained it with a 12-round nod over Juan Lazcano on June 5, 2004.

Following three successful defenses in his initial tenure as world champion, Castillo lost the title and a subsequent rematch to unbeaten Floyd Mayweather in April and December 2002. Many felt he got jobbed and that Mayweather was fortunate to get the nod in their first match.

After turning pro at age 16 in May 1990, Castillo knocked out his initial 14 opponents and won three titles before earning the WBC world crown. The 15-year veteran won the Mexican state featherweight (Oct. 2, 1992), Pacific 130-pound (Aug. 15, 1996) and Mexican featherweight (July 4, 1997) championships during the early part of his career.

Diaz (30-2, 22 KOs), of Coachella, Calif., was scheduled to make his first defense against Levander Johnson, but voluntarily relinquished his IBF belt for the opportunity to face Castillo.

“This is a mega-bout, the kind I have always desired,” Diaz said. “I could not pass up the chance.”

Diaz captured the IBF lightweight title in his last start when he won a majority 12-round majority decision over defending champion Javier Jauregui on May 13, 2004,in San Diego. Many thought the decision should have been unanimous.

“Nothing has ever come easily for me, but I have learned to roll with the punches,” Diaz said. “I was supposed to fight Castillo once before, but he backed out. I respect him now for acting like a true champion and taking this fight. These are the kinds of fights the fans deserve to see.

“I have always wanted to fight somebody who is really dangerous, where all the odds are against me, and I then I would beat them in an impressive way. This is my chance. It has nothing to do with money. I took the same fight a few years ago for practically nothing. I am really looking forward to March 5 and fighting Castillo on SHOWTIME.”

The talented Diaz, 25, who can box or bang, has been highly regarded for the majority of his career. Even before he won a world title, many observers considered him to be the best in the 135-pound division and one of the most promising young fighters in any weight class.

After going 185-15 in the amateurs, he turned pro in February 1999. He was USA Today’s “Prospect of the Year’’ in 2000. The brother of junior welterweight contender Antonio Diaz and retired former contender, Julio, won his initial 23 fights before losing a disputed 12-round split decision to the more experienced Angel Manfredy on Nov. 6, 2001.

Diaz has won six in a row, including the decision over Jauregui by the scores of 118-110 twice and 114-114.

“I thought I won that fight easily,” he said. “I was a little shaky when they were reading the official scores, but quite relieved and thankful to get the victory and my first world belt.”

Lacy (18-0, 14 KOs), of Tampa, Fla., will make his 12th appearance on SHOWTIME and his second defense of the IBF 168-pound belt he won with an impressive eighth-round TKO over Syd Vanderpool Oct. 2, 2004, on SHOWTIME. The first 2000 Olympian to win a world title, Lacy retained his crown the first time with a hard-fought 12-round unanimous decision over Omar Sheika Dec. 2, 2004, on SHOWTIME from Mandalay Bay.

“I just want to fight often and win,” said Lacy, who outpointed Sheika 117-111 and 115-113 twice. “This guy is coming to take something away from me, and it is my job to keep him from doing it.’’

Lacy went 209-12 in the amateurs, won numerous competitions and made it to the second round of the 2000 Olympics.

Williams (26-1, 15 KOs), of Detroit, Mich., fought Lacy as an amateur, going 1-2.

“I knew that one day that I would get another shot at him,” Williams said. “I thought I won all three fights against him. To get another shot at Lacy for his championship belt is very exciting. It is every boxer’s dream to fight for a world title.

“I am a boxer through and through. I love the chess match. I know I can keep him at bay with the left hand. But I have got some power with the right hand, too. I am going to kick’s Lacy’s butt.”

Williams has done some stomping in recent bouts, and has been victorious seven consecutive times since suffering the only defeat in his career. In his last outing, he retained his International Boxing Union Intercontinental 168-pound title with a 10-round decision over Aaron Norwood on Jan. 28, 2005, in Warren, Mich. Williams won his initial 19 starts after turning pro in August 2001. He captured the IBU Intercontinental crown with a 10-round decision over Tim Bowe on Oct 8, 2004, in Warren.