Mutton, a former international class freestyle and rodeo paddler, headed defending champion Jamie Sutton in the semifinal, with Sutton looking to win three titles in a row. Fox had earlier squeezed past John Snook, who won the inaugural Wairoa Extreme title in 1998, in the other semifinal.
Urwin, meanwhile, had to get a monkey off her back before claiming the title, edging Auckland's three-time winner Toni George in the women's final.
"I've got quite a few second-placings going back eight years or something," the 32-year-old said. "Last time I made the final [in 2011] was also against Toni and I was winning, then she just got me at the bottom. It was nice to get one back on her but to be honest anyone could've taken it today because the girls coming through in New Zealand are some of the best racers in the world. There's such a high level of paddling, because they're always paddling together and pushing each other."
Urwin spent the end of 2012 chasing massive water in Chile at the Whitewater Grand Prix and has not lost her edge over summer in Rotorua.
"I feel like I've been fitter but I'm paddling really strongly. I was in pretty good shape going into Chile and I've done a lot of stuff in the last year so I'm feeling pretty good."
In the semis Urwin beat Kim Dodd, while George slipped past double Olympic slalom representative Luuka Jones.
The race is part of the New Zealand Extreme Race series, which also features the Citroen Extreme Race on February 23 in Queenstown and the Buller Festival Boater Cross on March 1 in Murchison.