Vettori (18-4-1) handed Costa (13-2) his second consecutive defeat, scoring a unanimous decision victory in a light heavyweight matchup at UFC Fight Night inside the Apex. All three judges scored it 48-46 for Vettori.
The bout was originally scheduled to take place at middleweight, where both men are highly ranked, but it was changed to 205 pounds late this week after Costa arrived in Las Vegas heavy.
Costa, 30, proved to be in good condition and looked properly motivated, but Vettori's versatility and pace proved to be too much to overcome.
"Another improving experience," Vettori said. "I know I have the biggest heart and biggest will. When it goes to fourth and fifth rounds, there is no way nobody can keep up. A lot of people said he wouldn't be ready, but I feel a lot of it was a trick. He actually came pretty ready."
UFC president Dana White said he believes Vettori weighed 208 pounds for Saturday's fight while Costa weighed 220, adding that Costa will have to fight at light heavyweight moving forward.
Costa acknowledged afterward there was an issue in camp that prevented him from training for a bit, saying he had an injury to his left biceps, which is why he came into Las Vegas heavier than normal. His manager, Wallid Ismail, told ESPN he intends to speak to the UFC and White about keeping him at 185 pounds. Costa said he is open to the idea of competing at 205 pounds, but Ismail says he can still compete and safely make 185 pounds.
Vettori, who was coming off a loss to defending middleweight champion Israel Adesanya in June, pushed the pace from the opening bell. He took the center of the cage immediately at the start of each round and maintained a high volume of strikes throughout.
Costa, of Brazil, answered with some very hard power shots, however, and appeared to have Vettori hurt in the second and fourth rounds. He matched Vettori's pace early on, throwing hard body kicks and right hands. Costa seemed to fade in the middle of the fight, at times, before coming on hard in the fifth.
A well-placed right head kick rocked Vettori in the second round, and Costa looked for a finish. Vettori has never been finished in his career though, and he eventually got his feet back under him. Costa was deducted a point late in that second round after landing an accidental eye poke.
White praised Vettori afterward, saying he is the reason Saturday's fight went on.
"We were trying to keep this fight alive [this week], and we couldn't have done it without a guy like Vettori," White said. "Vettori acted like an absolute professional, stud. The guy was incredible to work with this week. He is why this fight happened."
It's a big win for Italy's Vettori, who had a five-fight winning streak snapped by Adesanya. He has lost to Adesanya twice, but Vettori has said he is seeking a third fight against him.
Costa has now dropped two in a row after beginning his professional career with 13 consecutive victories. This was his first appearance of 2021.