LAS VEGAS -- Any attempt to choose the most dominant active fighter in mixed martial arts inevitably leads to a choice between two champions: Jon Jones or Amanda Nunes.
Any discussion of the greatest fighters in MMA history must include Jones and Nunes as well. They simply have been too good for too long — and beaten too many fellow giants of the sport — to be left out.
When they fight on the same card Saturday night in Las Vegas, the joint showcase provides an opportunity for fans to see greatness at its possible peak. UFC 239 is also another chance to see whether Jones or Nunes will finally fall from the perches they have occupied for so long atop MMA.
"It only takes one fight, one punch, one slip to change a lot of things," Jones said this week.
Right before Jones (24-1, 1 no-contest) defends his light heavyweight title against Brazil's Thiago Santos (21-6) in the main event at T-Mobile Arena, Nunes (17-4) faces former champion Holly Holm (12-4) in the fourth defense of her bantamweight belt.
While Jones and Nunes are both favored to win, their matchups come with significant worries. Both challengers overcame major obstacles simply to reach this stage, and they're unlikely to be daunted by the aura of the greats standing across from them.
"He has a lot of great accomplishments, but he's just a man like me," Santos said. "I know what we need to do to beat him."
Santos was a middleweight less than a year ago, but he moved up to light heavyweight last September and promptly knocked out three straight opponents to earn this title shot. His 8½-inch reach disadvantage against Jones could be his biggest obstacle, because Jones knows how to use his oversized frame to full advantage against any opponent.
Santos is an extremely muscular light heavyweight, and he likely has more raw punching power than anyone Jones has faced recently. The champ is appropriately wary of the prospect of an early knockout.
There also is the small possibility of fatigue becoming a factor. Jones, who turns 32 later this month, is in his third fight in just over six months. He is still making up for the lost time and income of his late 20s, when he managed to be eligible for just four fights in a five-year span amid numerous failed doping tests and outside-the-cage misbehavior.
"It's a really good story, I know," Jones said. "It has its drama, and I'm hoping it has a happy ending."
Nunes is fighting for the first time since she became a two-division champion with her stunning 51-second knockout of Cris "Cyborg" Justino. Although Holm has lost four of her last six fights, she got this title shot on the strength of her talent and the fame that still lingers from her shocking upset of Ronda Rousey nearly four years ago.
Holm was a professional boxer for years, but Nunes is a formidable puncher who easily dispatched the aggressive Cyborg. Holm isn't likely to wade into an immediate brawl, as Cyborg did, and her kickboxing acumen is likely to force Nunes to be more patient.
But Nunes has shown the discipline and mental toughness to stick to a game plan, and Holm will be forced to be resourceful.
"I'm ready for anything she can bring to me," Nunes said. "We've studied her, but more important, I know what I need to do. I've been here before."
The two title fights are just the main attractions on a star-studded card for the UFC's annual International Fight Week pay-per-view show. Here are more things to know about UFC 239:
SHUT HIM UP: The biggest personal grudge on the card is between unbeaten welterweight Ben Askren and veteran challenger Jorge Masvidal. They have exchanged insults throughout the promotion of a fight that's likely to lead to a title shot for the winner. "In all my fights, I've never had this many people come up to me and beg me to end a guy," Masvidal said. "I had somebody ask me to turn his face into a sinkhole, to leave one side of his face no longer looking like the other side."
RETURN OF THE ROCK: Former middleweight champ Luke Rockhold makes his light heavyweight debut in his return from a 17-month absence against Poland's Jan Blachowicz. Rockhold believes he can easily beat almost anyone at 205 pounds, but Blachowicz is a powerful puncher.
GO DIEGO GO: UFC veteran Diego Sanchez has been in rare form before his showdown with Michael Chiesa, cutting wrestling-style promos and theatrically staring down his opponent at every opportunity. The brawl-loving Sanchez is rarely in a boring fight, but Chiesa has looked dangerous with his move to welterweight.
GILBACK: Gilbert Melendez hasn't won a fight since October 2013, but the loquacious 37-year-old veteran returns from a 22-month absence to fight Arnold Allen in the final preliminary bout on ESPN before the pay-per-view show begins.
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