Farrar, who claimed his first stage win of the season in the opening leg, completed the 189.7-kilometre fifth stage from Breckenridge to Colorado Springs in three hours 58 minutes 27 seconds.
"We had to use up a lot of our guys," said 2011 Tour de France stage winner Farrar, referring to team-mates who set him up for the sprint.
"That's putting a lot of faith in me because we're trying to win the GC (overall title)."
The stage took place as riders, teams and fans were coming to terms with American Lance Armstrong being stripped of his record seven Tour de France titles and being banned for life by the United States Anti-Doping Agency.
Van Garderen, who rides for the BMC team based in California, finished 14th in the same time as Farrar. He won the second stage to assume the lead via a tiebreaker and then regained it via a stage placing tally tiebreaker in stage four.
American Christian Vande Velde, Farrar's team mate for the American-based Garmin-Sharp team, placed 29th in the same time as Van Garderen and has the same overall time as the race leader.
However, Vande Velde has lower overall total stage placings.
Ivan Rovny of Russia remained third in the overall standings, trailing by six seconds.
Defending champion Levi Leipheimer of the United States is fourth overall, trailing by eight seconds.
A group of eight riders, including Italy's Vincenzo Nibali who was third in last month's Tour de France, built nearly a six-minute advantage.
The leading group, including Nibali, was reduced to three with 11 kilometres remaining. But the main field caught the trio on the concluding circuits around the finishing city.
The week-long race continues Saturday with 165.5-kilometre sixth stage, which includes the final two climbs of the seven-stage race.