Swanson got off to a slow start in the opening seconds and was even taken down by Oliveira inside of the first minute, but he was able to get back to his feet, and from there, his hands did the rest.
The finishing sequence started with a digging left hook to the body. Oliveira visibly cringed and Swanson came over the top with a blasting right hand. Oliveira staggered back two steps and then crashed down to the canvas.
The knockout came at 2:40 of the first round.
Oliveira had to be attended to by the cageside physician for a few minutes until he got back to his feet. Even then, he was unsteady and needed to be helped off by his cornermen.
"One big punch and they're going down for sure," Swanson said afterward.
With his third straight win, Swanson is now 18-5 and making waves in the featherweight division.
Oliveira had his two-fight win streak snapped and is now 16-3 with 1 no contest.