Santiago earns decision over Donaire for vacant bantamweight title
Santiago, 27, claimed the first world title of his career as he denied the 40-year-old "Filipino Flash," who was aiming to rebound from a brutal second-round knockout loss to Japan's Naoya Inoue 13 months ago.
Donaire, who has held world titles at flyweight, bantamweight, super-bantamweight and featherweight, kept it close in the early going and rocked Santiago with a left hook in the third round.
But he couldn't match Santiago's pace as the fight progressed, the Mexican landing a barrage of convincing blows in the ninth round and quickly halting Donaire's momentum when the Philippines fighter came out looking to land a big blow.
One judge scored the bout 115-113 and the other two saw it 116-112 for Santiago, who improved to 28-3 with five drawn and 14 knockouts.
"It's been an honour to fight such a legend like Nonito Donaire," said Santiago, who was brought to tears in the ring as Donaire offered a congratulatory hug in the ring.
Donaire fell to 42-8 with 28 knockouts and said he thought he had more to do in the ring.
"Disappointed," he admitted but added: "I feel good still. I love the sport so much."
He said he and his wife, Rachel, who trains and manages him, will have a conversation to "see where we go from there.
"But I know I felt good," he said. "There were just some things that didn't trigger."
Was that because he's 40 years old, Donaire was asked.
"I say 'Hell no' to that," he said.
The fight at T-Mobile Arena was on the undercard of the highly anticipated welterweight world title unification bout between unbeaten Americans Errol Spence and Terence Crawford.