The 35-year-old Ugas (27 wins, 4 defeats) threw fewer punches than Pacquiao (67-8-2), but his blows were more precise. Pacquiao struggled to get inside Ugas's jab, while the champion landed his right hand to increasing effect in the later rounds.
Two judges scored it 116-112 for Ugas, and a third had it 115-113.
After an unimpressive performance in his return from the longest layoff of his 25 years career, Pacquiao said he has not decided whether he will fight again. He also wouldn’t confirm whether he will enter the Philippines’ presidential race, as is widely expected.
“Let me rest first before my family and I make a decision,” Pacquiao said.
The victory was the culmination of a lengthy journey for Ugas, who defected from Cuba two years after winning a bronze medal in the Beijing Olympics. Ugas quit boxing for two years midway through the last decade, but recovered his career and capitalised on this unexpected shot against one of the greatest fighters of this era, earning his 12th victory in 13 fights.
“I’m very excited, but most of all, I want to thank Manny Pacquiao for giving me this moment in this ring today,” Ugas said through a translator. “We only had two weeks of training, but I listened to my corner and it all worked out.
“He’s a great competitor, but I came in here to show I am the champion of the WBA. A lot of respect for him, but I won this fight.”
Ugas got this opportunity only last week when Spence was forced to drop out after discovering he had a torn retina during a pre-fight physical. Ugas had been booked on the undercard, but he seized the opportunity for the spotlight and payday that had been just out of reach since he left Cuba on a small boat bound for Mexico 11 years ago.
T-Mobile Arena appeared to be sold out despite the late opponent change, and the crowd of 17,438 was behind their Filipino hero.
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.