Van Garderen, the BMC Racing Team rider from Bozeman, Montana, who took the overall lead with a second-place finish in the fourth stage, completed the 10-mile uphill time trial in 25 minutes, 1 second.

Van Garderen, 4 seconds ahead at the start of the stage, opened a 1:30 lead over teammate Mathias Frank of Switzerland. Van Garderen won the Tour of California in May.

"I was surprised I won the stage," van Garderen, who has held the race lead of the event twice in previous years but finished third and second overall. "I struggled in the last 2 kilometers. But I got the win and what's done is done and that's what matters."

American Andrew Talansky of Garmin-Sharp was second in the stage. Countryman Tom Danielson, also of Garmin-Sharp, was third overall, 1:42 back, after finishing third in the stage.

Van Garderen, who finished fifth in the 2012 Tour de France, led the inaugural USA Pro Challenge in 2011 but struggled on the same time trial course, finished sixth and lost the race lead.

"The race has been elusive," van Garderen said. "I took my until today to forget that ride in 2011."

Only two stages of the weeklong event remain, with a moderately challenging climb midway through the sixth stage as the only potential obstacle for van Garderen.

"There's a ton of things that can go wrong, a crash and Tom (Danielson) could go up the road with 20 guys," van Garderen said. "But I don't want to start listing things. I have confidence in my team that we can take it to Denver."

Danielson, who won the Tour of Utah on Aug. 11, nearly conceded and joked about poisoning van Garderen's water bottles and carrying a bicycle tire pump.

"I will go down swinging to the end," Danielson said.

Defending overall champion Christian Vande Velde, riding for Garmin-Sharp, had his best showing of the event, finishing ninth in the stage in 26:25. Vande Velde, competing in the last race of his career in the United States, was 21st overall - 6:54 back.

Tour de France champion Christopher Froome, the British star riding for Sky, continued his sub-par race, placing 49th in the stage. He weas 82nd overall, 38 minutes behind.

The race continues Saturday with a 115.2-mile leg from Loveland to Fort Collins, and will end Sunday with the 72.4-mile Denver Circuit Race.