Watched by Kiwi UFC star Israel Adesanya, who trains with Ahio and Fa at Auckland's City Kickboxing gym, Fa quickly got into his work against Ouatah in the main event.
Ouatah, who entered the ring with a 16-2 professional record, was taller than Fa and possessed a longer reach but Fa began aggressively and made his decisive move when connecting with a solid right hand after a clinch which caught his opponent unawares.
It was the first of four times that Ouatah went to the canvas before the referee mercifully ended a very short and one-sided contest. Fa is now 17-0 as a professional.
The victory suggested Fa is back to his physical best after health issues last year and it also suggests he has re-discovered a mean streak that appeared to go missing about the same time.
Ranked No8 by the WBO, Fa has talked about wanting a world title challenge this year and while he will face tougher opponents, he did what was expected and in convincing fashion.
In an interview with the Herald afterwards, Fa said the punch off the clinch, a potentially devastating weapon, was something he had been working hard on.
"It's become second nature to me," Fa said. "I did the same in my last fight. It's something I've been working on for the last year and I'm finally starting to use it properly. It's working.
"I feel great about the performance – I think it's a pretty good statement."
Fa will return to New Zealand while his next fight is negotiated – it will probably be in the United States given his deal with American promoter Lou Di Bella. He will also spar with Deontay Wilder ahead of the WBC world champion's next title defence.