Gambles won the race in 2011, setting the course record at 3 hours, 45 minutes and 35 seconds. Then last year, he broke that record winning again in 3:44:04.
The 31-year-old triathlete said he'll try to defend his title again this year, but said he plans to race smarter in Boulder this year so he can get results at the 70.3 world championships in Las Vegas in September.
"I sort of left my season at Boulder the last couple of years," he said. "I've raced really well at Boulder... I want to do well and I want to defend my title, but it's really about Vegas."
In 2011, Gambles finished 5th at the world championships and then in 2012, finished 12th. This year will be different, he said.
A stacked pro field with athletes like Greg Bennett, Jordan Jones and Gambles' own training partner, Ben Hoffman, will make it more difficult for Gambles to win again.
"We're giving each other a hard time," said Gambles, of competing against Hoffman.
In early July, the two shared a horrifying training ride together with their friend and fellow triathlete Richie Cunningham. The three were riding north on 83rd Street when a car passed the duo, then slammed on its brakes. Cunningham braked hard, flipped over his handlebars and ended up breaking his elbow and separating his shoulder. Hoffman tracked down the car and wrote down its license plate, though no charges were filed against the driver.
For the three training partners, Cunningham is the "glue" that holds everyone together, Gambles said, so watching him go down was extremely difficult.
"Ben and I both had a really tough time," Gambles said. "The week after that we lost all motivation. I just didn't have that spark. It shook us up for sure."
Cunningham is doing well, Gambles said, and is rehabbing from his injuries. He should be back to racing by the end of September.
For Hoffman, who won and set the course record at Ironman Coeur d'Alene earlier this summer, seeing his friend taken out for a good chunk of his season by an angry driver made him appreciate his friendships with Cunningham and Gambles more, Hoffman said.
"It made all of us more aware of how we rely on each other for training motivation and just how quickly things can change," he said. "All of us were enjoying a high point in our racing season and then suddenly it switches over and Richie is out for at least six weeks and back to square one. It has certainly give us perspective and made us appreciate the friendships more."
Gambles' course record will be thrown out after this year's 70.3 race because of a new bike course, said race director Dave Christen.
The bike course has been a double loop all contained within Boulder County, but starting this year, the bike leg will be a single loop that stretches up into Larimer County, Christen said.
Christen said the pending 2014 full Ironman race, which is scheduled for Aug. 3, 2014, has brought more excitement and interest to the 70.3 race. Christen said he's seen more training groups around town and Ironman has received a massive influx of people wanting to volunteer at the 70.3 race.
The women's professional field is also stacked for the Boulder 70.3 race, with athletes like 2012 Ironman world champion and 2012 70.3 world champion Leanda Cave racing for the win. She'll compete against 2011 Boulder 70.3 winner Angela Naeth and 2009 70.3 world champion and multiple-time Xterra world champion Julie Dibens, who hasn't raced for the last two years. Also scheduled to race is Melissa Hauschildt, the 2013 ITU Long Distance world champ.
"The women's field is just loaded," Christen said. "I look at the female field, and this just has to be one of the strongest female fields that we've had in recent history."
--Follow Sarah Kuta on Twitter: @SarahKuta.