LAS VEGAS — Although Manny Pacquiao hasn't decided what his future holds, the eight-division world champion realizes his 26-year professional boxing career might have ended Saturday night with a disheartening loss.

Yordenis Ugás is only seven years younger than the Filipino senator, yet he's just getting started after seizing this improbable opportunity to knock off one of the greats.

Ugás beat Pacquiao by unanimous decision in Las Vegas, putting on an impressive technical performance on 11 days' notice and retaining his WBA welterweight title.

"He's a great competitor, but I came in here to show I am the champion of the WBA," Ugás said. "A lot of respect for him, but I won this fight."

Ugás (27-4) capitalized on this chance as the late injury replacement for Errol Spence Jr.. The Cuban veteran was slightly better than Pacquiao (67-8-2) throughout one of the most frustrating fights in the 42-year-old Filipino senator's career.

"I did my best tonight, but my best wasn't good enough," Pacquiao said. "No excuses. I wanted to fight for the title in the ring, and tonight the champion is named Ugas."

A visibly disappointed Pacquiao said he hasn't decided whether he will fight again after an unimpressive performance in his return from the longest layoff of his quarter-century in the sport. He also wouldn't confirm whether he will enter the Philippines' presidential race, as is widely expected. He intends to make an announcement next month.

"In the future, you may not see Manny Pacquiao again to fight in the ring," Pacquiao said. "I don't know, but I'm so happy for what I've accomplished."

The 35-year-old Ugás threw roughly half as many punches as Pacquiao, but his blows were more precise and more effective. Pacquiao was the solid favorite before the bout, but he struggled to get inside on Ugás' effective jab while Ugás landed his right hand to increasing effect in the later rounds.

Two judges scored it 116-112 for Ugás, and a third had it 115-113. The Associated Press also scored it 116-112 for Ugás.

Pacquiao also said his legs were cramping from the second round onward. He attributed the problem to a combination of overtraining and age.

"I think it was too much hard work," Pacquiao said. "But I'm not young anymore. So I don't know."

The victory was the culmination of a lengthy journey for Ugás, who defected from Cuba two years after winning a bronze medal in the Beijing Olympics. Ugás quit boxing for two years midway through the last decade, but revitalized his career and then capitalized on this golden chance by earning his 12th victory in his last 13 fights.

Ugás was in the spotlight only because Spence was forced to drop out last week after discovering he had a torn retina during a pre-fight physical. Ugás had been booked for a bout on the undercard, but he jumped at the type of showcase and payday that had been just out of reach ever since he left Cuba on a small boat bound for Mexico 11 years ago.

"I'm very excited, but most of all, I want to thank Manny Pacquiao for giving me this moment in this ring today," Ugás said through a translator. "We only had two weeks of training, but I listened to my corner and it all worked out."

T-Mobile Arena appeared to be essentially sold out despite the late opponent change, and the crowd of 17,438 was vocally behind its Filipino hero. Even after a lengthy layoff in the last stages of his career, Pacquiao remains a surefire draw and a bankable star in a sport lacking both at its highest levels.

Ugás had a clear game plan on short notice, working hard in the early rounds with an effective jab and body shots. Pacquiao was more aggressive and occasionally got the crowd to its feet with combinations, but Ugás' rangy jab stymied him.

Ugás' confidence grew in the middle rounds, and he responded to some action at the seventh-round bell with a defiant shimmy-shake of his shoulders in Pacquiao's direction. Pacquiao constantly threw more punches than Ugás, but they landed about the same number as Ugás showed off his defense and accuracy against Pacquiao's activity.

Pacquiao caught Ugás with a combination in the 10th round and knocked him back as the crowd rose in excitement, but Ugás recovered and rallied with big shots. Ugás also looked sharp in the 12th round, peppering Pacquiao all the way to the final bell.

Pacquiao had won three straight bouts since July 2017, but he hadn't fought since beating Keith Thurman in 2019 to win the WBA welterweight title.

That belt belonged to Ugás by the time Pacman returned: While Pacquiao's political career and the pandemic kept him out of the ring in 2020, the WBA took away the belt and awarded it to Ugás, who had won a different version of the belt in the WBA's byzantine championship system.

The WBA's decision irked Pacquiao, who held various welterweight belts for a decade after he first moved up to 147 pounds in 2009 and stopped Miguel Cotto in arguably his single greatest performance.

On the undercard of Ugás' victory at T-Mobile Arena, Robert Guerrero returned from a 23-month ring absence with a unanimous decision over fellow veteran Victor Ortiz, winning 96-94 on all three cards.

The 38-year-old Guerrero (37-6-1) had a strong second round and persevered with a high punch volume to beat the 34-year-old Ortiz (32-7-3), who hadn't fought in 42 months. Ortiz was charged with multiple counts of sexual assault in 2018, but the charges were dismissed late last year.

Filipino featherweight Mark Magsayo (23-0, 16 KOs) also preserved his unbeaten record with a dramatic 10th-round knockout of Julio Ceja, who was ahead on all three judges' scorecards.