Dos Santos (20-5) absorbed a nasty low leg kick in the opening round, which appeared to hamper his mobility early on. He regrouped in the second frame, however, and capitalized on a huge shift in momentum about a minute in.
The finish came at the 2:40 mark, after dos Santos surprised Tuivasa (8-2) with a short right hand. Rather than take a step back, Tuivasa aggressively pressed forward to get dos Santos back, but he ended up eating three more blows, the last of which knocked him to the canvas.
"My game plan is always my punching," dos Santos said. "I have knockout power, and I can knock anyone out."
Referee Herb Dean did not stop the bout immediately after Tuivasa went down. Tuivasa tried to recover, but dos Santos moved into full mount and dropped more punches until the bout was stopped. Tuivasa couldn't escape but tried to throw punches from his back in an effort to keep it going, but Dean had seen enough.
Dos Santos, who has now won back-to-back fights, called for a rematch against Alistair Overeem, who knocked him out in December 2015.
"Anyone, any of the big opponents everybody knows," dos Santos said. "I think a rematch with Alistair Overeem would be very good right now."
Dos Santos missed the second half of 2017 due to a failed drug test, which was ruled to be caused by a contaminated supplement. He has defeated Tuivasa and Blagoy Ivanov since his return this year.
Hunt suffers lackluster loss in final fight on UFC contract
Hunt, 44, was an interesting figure going in, as he was on the last fight of his contract. The New Zealand native has butted heads with the UFC in recent years and even filed a civil lawsuit alleging that the company knowingly allowed Brock Lesnar to dope ahead of a fight in 2016.
Willis (8-1) easily outpointed Hunt on the feet en route to unanimous 29-28 scores. Hunt landed a few early kicks but abandoned them after a cut opened on his shin. Willis peppered him with the jab during the final two rounds and sidestepped the occasional haymaker.
"Apologies on my performance," Hunt said after the fight. "Thank you for your support, all Australian people, New Zealand people. Thank you, UFC. I'll see you somewhere else."
Hunt debuted with the UFC in 2010. The promotion initially offered to buy him out of his contract, which it acquired in its purchase of Pride Fighting Championships, but Hunt wanted to prove that he could compete. He went on to an 8-8-1 record and fought for the title in 2014. He has said multiple times that he intends to continue his career in another promotion.
Former champ Rua scores upset victory
Former light heavyweight champion Mauricio "Shogun" Rua (26-11) shocked Tyson Pedro (7-3) in a third-round TKO upset to improve to 4-1 in his past five contests. The finish came via strikes on the ground at the 43-second mark.
A more than 4-1 betting underdog, Rua survived a clash of heads in the opening round before seizing momentum. He dominated Pedro from top position in the second round and hurt him with an early right hand in the third.
Pedro, 27, appeared to suffer a leg injury just before the finish. The Australian stepped back awkwardly after eating a punch and was eventually finished as he covered up along the fence.
It's a massive result for the 37-year-old Brazilian, especially after he was badly hurt in the first round. It is the 21st knockout of his illustrious career.
"Tyson is a great fighter, well-rounded, very tough guy," Rua said. "One more win, and I am [going] for the belt."