LAS VEGAS -- Israel Adesanya's meteoric rise to UFC superstardom hit a rather large obstacle Saturday night.

Jan Blachowicz beat the previously undefeated Adesanya by unanimous decision (49-46, 49-45, 49-45) to retain his light heavyweight title in the main event of UFC 259.

Adesanya, the UFC middleweight champion, was attempting to become just the fifth fighter in UFC history to hold two titles concurrently.

"It didn't go exactly the way I wanted it to go, but dare to be great," Adesanya said. "You know, the critics are the ones on the sideline, but I'm the one putting it on the line."

Adesanya added: "If I was gonna lose to anyone, I'm glad I lost to him. Credit to him. He's a great champion."

The story of the fight leading in was that Blachowicz would have a significant size advantage. Adesanya tipped the scales at 200.5 pounds during Friday's weigh-in, 4.5 pounds under the 205-pound limit for a light heavyweight title fight. Blachowicz weighed 205 pounds and said he planned on competing Saturday at 220 pounds.

Adesanya, who typically competes in the 185-pound division, likely didn't gain much weight from weigh-ins, meaning Blachowicz would be about 20 pounds heavier in the Octagon.

"Size is always a factor when you move up a weight class in this sport," UFC president Dana White said. "It was definitely a factor. Weight was a factor. When you move up a weight class like that, strength is a factor. How hard these guys hit is a factor. And Jan is the real deal."

That size disparity paid dividends for Blachowicz. The Polish fighter took over the fight late with big takedowns in the fourth and fifth rounds. Adesanya seemed to be building some momentum in the fourth when Blachowicz exploded in for a double-leg takedown. Both times, Adesanya could not get up. While Blachowicz didn't do a ton of damage on the mat, he held Adesanya there very effectively and sprinkled in some punches.

As the clock was expiring to end the fight, Blachowicz finally landed some hard hammerfists and advanced into full mount. The final flurry all but sealed the bout.

"When I took him to the ground, he felt the difference between his category and [light heavyweight]," Blachowicz said.

Adesanya said it was Blachowicz's defensive skills, not his size, that might have been the difference Saturday night.

"I wouldn't say size, because I can hurt big dudes," he said. "I think it was just his defense. He was really tight with his defense and smart with his defense."

Judges Derek Cleary and Sal D'Amato gave Blachowicz every round except for the third, and Cleary gave Blachowicz a 10-8 in the fifth. Judge Junichiro Kamijo gave Blachowicz every round except the second and also scored the fifth 10-8 for him.

Blachowicz had a 107-78 edge in significant strikes, outlanding Adesanya in every round, including 28-12 in the fifth.

"This guy is a tough guy," White said of Blachowicz. "You've seen all the guys Izzy has fought and what he's done. Jan is a tough guy."

Coming in, ESPN had Adesanya ranked the No. 4 pound-for-pound MMA fighter in the world. Adesanya is ranked No. 1 at middleweight, while Blachowicz is ranked No. 2 at light heavyweight, behind only all-time great Jon Jones, who is currently moving up to heavyweight.

UFC 259 took place with COVID-19 protocols in place inside the UFC Apex, a facility across the street from the promotion's corporate campus.

Blachowicz (28-8) has won five bouts in a row. He claimed the UFC light heavyweight title in beating Dominick Reyes by second-round TKO at UFC 253 in September. Blachowicz, 38, has won nine of 10 fights overall and has had a pretty incredible late-career surge. He has been a pro since 2007, and he was the light heavyweight champion of his home country's KSW promotion in 2011.

"Everybody is different. I just found a way how to be the best," Blachowicz said of his late success, adding, "No question, I'm the best. I'm the best in the world."

Adesanya (20-1), a former champion kickboxer, won his first nine fights in the UFC before Saturday. The Nigeria-born New Zealand resident is coming off a second-round TKO over Paulo Costa at UFC 253, in the headlining fight of the card in which Blachowicz won the light heavyweight title. The flashy Adesanya, 31, has 15 knockouts in 20 career wins and has been UFC middleweight champion since October 2019.

Blachowicz entered Saturday's main event as a plus-210 underdog, according to Caesars Sportsbook by William Hill. In the past 10 years, no fighter has more wins as a betting underdog than Blachowicz, who is tied with Neil Magny and Andrei Arlovski with eight.