Jonathan Ndambuki struggled against freezing rain and wind to win the Denver Marathon on Sunday by 13 seconds over fellow Kenyan Charles Kiplagat with an unofficial time of 2 hours, 21 minutes, 34 seconds.
The temperature was 1 C (34 F) when the race began.
"You cannot move very fast. It was tough," Ndambuki said. "I even started freezing a little."
The countrymen traded the lead until Ndambuki broke away in the 37th kilometer (23rd mile).
Martha Tenorio of Boulder won the women's race in 2:46:41.
Temperatures below 2 C (35 F) for most of the race and rain kept runners from achieving their best times, Ndambuki said.
Kiplagat wasn't prepared for the Colorado cold having just flown in from Kenya on Saturday.
"Wow," he said, cradling himself in a warming blanket. "It's too cold. It's chilly. You know I come from a hot place. Coming straight to colder place will affect you."