Aaron Simpson's welterweight debut was a success.

The wrestler out of Phoenix's Power Team MMA camp had mixed UFC results as a middleweight, but its so far, so good at 170 pounds.

Simpson grinded his way to a unanimous decision win over Kenny Robertson on Wednesday night at UFC on Fuel 4 in San Jose, Calif. The judges scored the bout 30-27, 29-28 and 29-28.

After a competitive and close first round, Simpson took over in round two, using his wrestling to stymie Robertson, who was a replacement for an injured Jon Fitch.

Simpson turned it on in round three and appeared close to finishing the fight in the closing seconds, but Robertson managed to hang on until the final horn.

The 37-year old Simpson improved to 12-3 and won for the fourth time in his past five fights.

"I gotta get used to it, gotta get used to these guys speed," Simpson said. "He's a scrappy guy, my hat's off to him. I'll be better. I gotta finish guys at this weight, that's what this business is built on."