Featherweight world titleholder Leo Santa Cruz has enjoyed a great deal of success. He's won world titles in three weight classes, had major fights with Abner Mares and Carl Frampton -- each of whom Santa Cruz faced twice -- and he's made several million dollars over the course of his career.

But he still has his eye on adding to his legacy. Santa Cruz badly wants to face the biggest names in boxing; he's desperate for a title unification fight; and he plans to eventually move up to junior lightweight to seek a title in a fourth division.

At this moment, Santa Cruz can't have any of those sort of fights, so, as he bides his time, he has taken a fight that's expected to be a routine defense. He'll take on replacement opponent Rafael "Big Bang" Rivera in the main event of a Premier Boxing Champions tripleheader Saturday (Fox, 8 p.m. ET) at the Microsoft Theater at L.A. Live in Los Angeles.

Santa Cruz has always been a respectful fighter with nothing bad to say about his opponents, though, and he is giving Rivera respect the same way he did with original challenger Miguel Flores -- even if the fight is viewed by most as a mismatch.

"We were getting ready for Miguel Flores, but in the gym you have to always be ready for any kind of style. We had already been working with sparring partners who brawl, and that's what we expect from Rafael Rivera," Santa Cruz said this week. "I knew immediately that Rivera was a good opponent. He's young and hungry, and that makes him dangerous. He can take punches, so we're ready for 12 rounds. We're going to be smart in this fight because we know what Rivera can do."

Flores (23-2, 11 KOs), Santa Cruz's original opponent, was also expected to be an easy night at the office -- but he dropped out about a month ago after suffering an ankle injury in training camp.

Rivera (26-2-2, 17 KOs), 24, of Mexico, is coming off a first-round knockout of Jose Ramos in October but lost two fights in a row before that, by split decision to unbeaten prospect Joet Gonzalez in July and then by lopsided decision to then-unbeaten contender Joseph Diaz Jr.

Since winning back his featherweight world title, Leo Santa Cruz has successfully retained it in fights against Chris Avalos and Abner Mares. Joshua Dahl-USA TODAY Sports

"Rafael Rivera has nothing to lose in this fight, and that is the recipe for a tremendous showdown," said Ringstar Sports promoter Richard Schaefer, the co-promoter of the card.

Rivera said he is ready to give his all in the unexpected shot at a world title.

"When I got this opportunity, I didn't think twice. I was training and ready, and I wanted this challenge. I'm here to make the most of it. I've stepped in late before to a big fight," said Rivera, who also took the fight with Diaz on short notice. "I'm always ready when it comes. Expect a surprise come Saturday night. I know that I have everything it takes to bring this title back to Tijuana. We've trained hard and had these last four weeks to focus in on breaking Leo down.

"I'm prepared for anything Leo brings into the ring. Everyone knows he's very tough and throws a lot of punches, but I believe I am the faster fighter and I can hurt him with counters. This is the best opportunity I've had, going up against a great champion like Leo. I'm ready for a fight and a great show for the fans."

Santa Cruz (35-1-1, 19 KOs), 30, of Los Angeles, who will be making his third defense of this title, is coming off a decision victory over Mares, whom he outpointed for the second time in an action-packed fight in June.

Although he has Rivera in front of him, Santa Cruz has not been shy about talking about the fights he really wants. No. 1 on his list is a unification bout with perpetually inactive Gary Russell Jr. (29-1, 17 KOs), 30, of Capitol Heights, Maryland. Russell fights generally only once a year, but there is a chance the fight will happen later this year on Showtime, which has pushed for the bout.

"Gary Russell Jr. is the fight that I want. He beat me in the amateurs, but in the pros I get 12 rounds," Santa Cruz said. "I think that I can beat him."

One of the big options in play for Leo Santa Cruz's future is a trilogy fight against Carl Frampton, after two tremendous title fights in 2016 and 2017, including Santa Cruz's only career loss. AP Photo/John Locher

If Santa Cruz can't get Russell to commit to the fight, he is also open to a title unification fight with Oscar Valdez or Josh Warrington. A Valdez fight is unlikely, given that he fights for Top Rank (on ESPN), but Warrington is possible. Santa Cruz is also interested in a possible third fight with Frampton, with whom he has split a pair of majority decision barnburners; Santa Cruz lost a featherweight belt to Frampton in July 2016, then regained it in the immediate rematch in January 2017.

Eventually, Santa Cruz plans to go up to 130 pounds, where he said he is interested in challenging titleholder Gervonta Davis in what would be a major fight.

"I'm just looking to go out there, give a great fight and help my name continue to grow so that I can fight the best," Santa Cruz said. "If I can get this win [over Rivera], we want to unify the belts or make the third fight against Carl Frampton. If not, we will go to 130 pounds and seek a title in a new weight class."

Jose Santa Cruz, Leo's father and trainer, is on board with his son's plan.

"Leo is 30 years old right now, and I think that he will be retired by 35," he said. "He has a lot left to accomplish in this sport, and our team is going to keep pushing him to be the best that he can."

Figueroa vs. Molina

In the co-feature, former lightweight world titlist Omar Figueroa Jr. (27-0-1, 19 KOs), 29, of Weslaco, Texas, faces former world title challenger John Molina Jr. (30-7, 24 KOs), 36, of Covina, California, in a 10-round welterweight bout most expect to be an all-out brawl.

"I don't think this goes past six rounds. I'm confident about that. We're going to be ready for anything Molina brings," Figueroa said.

"Given our styles, there's no way this is going to go the distance. I think this is going to be an early night, and I'm planning on having my hand raised."

"I think Omar's style will accommodate mine and make it a fun fight for the fans," Molina countered. "Whenever I fight, it's going to be exciting. You can say the same thing about Omar. I'm prepared for any version of Omar. Just like any other fight. I can't wait until Saturday night to get in there and do what I do best. This is going to be a war, and I believe we're going to steal the show."

Neither of them boxed in 2018. Figueroa is coming off a 19-month layoff because of injuries and a DUI arrest.

"The layoff didn't affect me against Robert Guerrero, so I don't see why it will affect me now," Figueroa said of the win he had in his last fight, in July 2017, which followed another 19-month layoff. "That's why I keep my style consistent. The only difference is the character across from me in the ring. This fight will depend on how John wants it to go, because I'm coming to fight. Training camp went great. I've made a lot of changes in my lifestyle, and I'm dedicated 100 percent to boxing."

Molina has been idle since his rousing fourth-round knockout of Ivan Redkach in December 2017.

Most recently, Molina had a September fight with Victor Ortiz canceled because of Ortiz's arrest on a rape charge.

"It's time to fight. The hard work is done, and the time is now. Talk is cheap. On Saturday night, we'll get down," Molina said.

In the televised opener, junior middleweight prospect Sebastian Fundora (11-0, 7 KOs), 21, of Coachella, California, and Donnie Marshall (10-0, 6 KOs), 30, of Raleigh, North Carolina, will meet in an eight-rounder. Fundora, a southpaw, is known as "The Towering Inferno" because at 6-foot-6 he is colossally tall for a 154-pound fighter.