"I wasn't expecting to win," Ortiz said. "I came in here just wanting to have fun and I mean it all came together. To win it is ten times better."
Paul Rodriguez of Tarzana, Calif., was second at 91.25, and Milwaukee's Greg Lutzka was third at 86.75. Three-time defending Dew Cup champion Ryan Sheckler finished 10th.
Earlier, Adam Jones won the Freestyle Motocross event and also took the Dew Cup.
The 24-year-old Jones, from Minden, Nev., took the lead in his first run and retained it throughout the event. He executed a stripper flip, a turntable and a KOD flip during the competition.
"I tried to tell myself I didn't feel any pressure, but I felt a fair bit of pressure," Jones said. "I didn't sleep at all last night. I was tossing and turning all night."
Australia's Robbie Maddison was second at 93.10, and Jeremy Lusk, from San Diego, was third at 92.57.
The four-day competition, which drew 53,566 fans, was the final event of the five-stop AST Dew Tour that features skateboarding, BMX and freestyle motocross.