Van de Kamp finished in 2 hours, 21 minutes, 14 seconds to beat Hunter and Kotter by just more than a minute. He added the St. George title to earlier wins in the Salt Lake City, Ogden and the Deseret News marathons.
"After [mile marker] 14, it was just me and Jon until 22 or 23," Van de Kamp said. "Then I slowly inched away from him and just held on at the end."
Van de Kamp suffered a hamstring injury shortly after winning the Deseret News Marathon on July 24. Although he did extensive cross-training to maintain his fitness, he ran only one 5K race before St. George.
"I wasn't able to get in a good half marathon about two weeks before, like I usually do," Van de Kamp said. "So I didn't feel totally prepared. I went into this one a little more nervous and less confident than the others."
Van de Kamp beat more than 6,000 runners in St. George.
"To win here is great," he said, "because it's such a big race and such a great event."
In the women's division, St. George's Amber Green scored an emotional victory in 2:43 five minutes better than her previous best time. "I wanted to break 2:45, and I've always had a dream of winning the St. George Marathon, to represent my city."
Green entered her hometown marathon eight times before winning.
Last year, she suffered a stress fracture four miles into the race and pulled out near the halfway point.
"It was devastating," said Green, who was motivated by the disappointment in 2011.
"This year I had a little bit of fuel under me. I wanted to finish what I started last year. So I had a lot of motivation, a lot of help from God and a lot of help from my family. They were so supportive of my training."
Green, a mother of three young children, felt a power surge when she passed the place on the course where she pulled out of last year's race.
"I thought, 'Amber, this is where you get to fly,' " she said. "And I just took off. ... Yeah, there was a lot of extra energy at that point."
Top five finishers
Men City Time
Fritz Van de Kamp Millcreek 2:21:14
Iain Hunter Provo 2:22:16
Jonathan Kotter Provo 2:22:45
Scott Keate Highland 2:22:53
Pepi Peterson Hudson, Mass. 2:23:29
Women City Time
Amber H Green St. George 2:43:00
Annie O'Donnell Upland, Calif. 2:52:19
Julie Thomas Salt Lake City 2:52:27
Katy Andrews Encinitas, Calif. 2:52:58
Arianne Brown Eagle Mountain 2:54:04