James Koskei of Kenya won the men's professional race in the Bolder Boulder on Monday.
He beat out countryman and defending champion Joseph Kimani who finished second in the 10-K road race.
Jose Castillo of Peru finished third.
Deena Drossin of Alamosa, Colo. was the winner of the women's professional race.
Drossin grabbed an American flag offered by a spectator as she entered Folsom Field for the final lap. The five-time national cross country champion said that she did it for everyone who was cheering for her in the stadium and out on the street.
Martin Weiss won the men's citizens race and Natalie Davey, an Irish national who lives in Boulder, finished first on the women's side.
Saul Mendoza won his fourth straight wheelchair title and Ariadne Hernandez won the women's wheelchair race.
The addition of a steep hill in the Bolder Boulder 10-kilometer race favored altitude-trained runners in Monday's 23rd annual event.
"It doesn't make the athletes feel any more comfortable, especially the athletes who come from sea level," elite race coordinator Rich Castro said before the race began.
"I told Jose Castillo of Peru that we've added another hill in the middle of the race and it should make it better for his team. He said, `Not necessarily.' A hill is a hill. When you're running hard, it can still take the wind out of your sails."
Runners in both the men's and women's elite races started in Folsom Field, made two laps on Folsom Street, returned to the stadium for a lap and then made three more laps on the street before finishing in the stadium.
The mid-course return to the stadium included a steep climb around the backside of the Dal Ward Center, which Castro noted is "a segment that no one has ever climbed before."
Frank Shorter, the 1972 Olympic marathon gold medalist and co-founder of the Bolder Boulder, said two factors entered into the course alteration.
"We wanted to have the people in the stadium see more of the race than they would otherwise," he said. "Our other thought was, previously you had to go up that hill to the stadium only once. Now we've introduced the psychology of climbing that hill twice. I think it's going to change the complexion of the race from a strategic standpoint."
A record 44,432 runners entered last year's citizens race, and race director Cliff Bosley said the number of entrants for Monday's event was closer to 45,000. In addition, police estimated around 100,000 spectators were on hand to watch the races.