Muniz, 23, parlayed a series of front-side turns on his first wave and backhands on his second ride to victory over American teenager Kolohe Adino by a score of 16.23-14.54.
"I knew I had to get scores and the waves were dying a little bit with the high tide and the ocean really cooperated with me today," Muniz said.
Adino, 19, started the final heat with a nifty 7.77 score but the flagging 1- to 3-foot Orange County surf did not produce a productive wave that would have allowed him to keep pace with Muniz, who breezed through the quarter and semifinals and jumped from 24th to 15th in the Association of Surfing Professionals points standings.
Earlier Sunday, Hawaii's Carissa Moore held off a late charge by Courtney Conlogue of the mainland U.S. 16.00-15.27 to win the women's division and take over the top spot in the ASP women's standings.
"I'm a little shocked right now because I thought Courtney [Conlogue] won when the crowd erupted on that last wave," Moore said. "I let her go and I had priority and it was a bad decision, but I'm stoked that it worked out in my favor."