He was sixth at the 20-mile mark but came on strong in the closing stages, passing Levy Matebo in the final mile to win by 26 seconds.

Korir's time of two hours, 12 minutes and 40 seconds was the second slowest in the race since 1985.

"When the guys took off I tried to go with them but they were taking off at a really hard pace. I knew that if I were to go too hard too soon to quickly, I'm going to cramp up," said Korir, who is married to Canadian runner Tarah McKay, lives in the United States and is seeking US citizenship.

"I was more concerned about myself because it's really, really hot out there. At that point I was like it's going to be better for me to be conservative and to be safe."

Matebo crossed the line in second place, seven seconds ahead of Bernard Kipyego.

Defending champion Geoffrey Mutai, who ran the fastest ever marathon last year at Boston and went on to win in New York as well, dropped out after 30 kilometres due to cramping.

Slow start

Kenyan athletes also claimed a clean sweep of the podium in the women's race, won by Sharon Cherop in two hours, 31 minutes and 50 seconds.

Cherop's margin of victory was two seconds from Jemima Jelagat Sumgong, with Georgina Rono over a minute further back in third.

"We started slowly, we did not start fast like last year," said Cherop, who finished third in 2011.

"I was really prepared this time around ... it's not my first time running in the heat and humidity."

Organisers warned novice runners not to race due to concerns about the heat but a field of 22,426 started the 26.2-mile course from 26,716 original entrants.