BOSTON — Wesley Korir, a Kenyan citizen and permanent resident of the United States, won the Boston Marathon on Monday in a heat-slowed time of 2 hours, 12 minutes, 40 seconds that was almost 10 minutes behind the world best established here a year ago by Geoffrey Mutai.
It was the second-slowest Boston race since 1985, as temperatures rising into the 80s slowed the leaders and may have convinced as many as 4,300 entrants to sit this one out. Mutai, who was hoping a repeat victory would earn him a spot on the Kenyan Olympic team, dropped out after 18 miles with stomach cramps.
Instead, Korir may have won a ticket to the London Games.
"To me, I think running the Boston Marathon is an Olympic event," the two-time Los Angeles Marathon champion said. "I don't care what comes up after this, but I'm really, really happy to win Boston."
Sharon Cherop won the women's race to complete the Kenyan sweep, outkicking Jemima Jelagat Sumgong to win by 2 seconds in 2:31:50. The women's race was decided by a sprint down Boylston Street for the fifth consecutive year.
The combined margin of victory in those five races is 10 seconds.
"I was thinking, maybe I would catch her," Sumgong said. "But she kept on pushing, pushing, pushing."
Levy Matebo was second in the men's race, 26 seconds behind the winner, and Bernard Kipyego finished third as Kenyans swept the podium in both genders. Jason Hartmann of Boulder, Colo., was in fourth place and the top American.
Korir was the 19th Kenyan men's winner in 22 years. But he is hardly typical of the African runners who have come to dominate the event since Greg Meyer became the last American winner in 1983.
Korir attended college at Murray State — the Racers, naturally — before transferring to Louisville and graduating from the school with a biology degree. He is hoping to receive American citizenship within a few years.
The winners will receive $150,000 apiece. Korir and his wife, Canadian runner Tarah McKay, run a foundation in his hometown of Kitale and have been building a hospital in the memory of his brother Nicholas, who was killed by a black mamba snake at the age of 10.
A total of 22,426 runners started the race in Hopkinton in temperatures expected to be as high as 84 by the time the last of them finish their 26.2-mile trek to Boston's Back Bay. That's about 84 percent of the registered field of almost 27,000, with many of the no-shows expected to take race organizers up on their offer for a deferment into next year's race.
The largely unprecedented offer was issued in response to forecasts that called for temperatures rising from 69 at the start to 81 by the midpoint.
The heat didn't seem to be a problem for Canadian Joshua Cassidy, who won the men's wheelchair race in a time of 1 hour, 18 minutes, 25 seconds that is the fastest in history. American Shirley Reilly edged Japan's Wakako Tsuchida during a sprint to the finish in the women's wheelchair division.
But the runners were content to pace themselves.
One year after cool temperatures and a significant tailwind — perfect running weather — helped Mutai finish in 2:03:02 for the fastest marathon ever, the heat had elite runners preparing for a slower pace and the recreational runners trying to figure out how to finish at all.
The wheelchair racers left Hopkinton at 9:17 under sunny skies and a temperature of 69 degrees, followed by the women's field at 9:32. It was 73 when the elite men and the rest of the field went off at 10 a.m.
The total field included 26,716 entrants, but 3,683 never picked up their bib numbers over the weekend. Another 607 who picked up their starting bibs did not show up at the start; they will be offered a chance to run in 2013 instead.
With forecasts of dangerous heat, the Boston Athletic Association warned runners to be alert for signs of heat stroke and dehydration and asked those who were inexperienced or ill to skip this race. The B.A.A. offered a limited deferment in 2010, when the Icelandic volcano eruption stalled air traffic in Europe and prevented about 300 runners from getting to Boston.
Five-gallon jugs of water — twice as many as usual, organizers said — were already lining the route early in the morning as volunteers and medical staff stood by preparing for the influx of hot and tired runners.
The Boston Marathon has had its share of hot weather, with the thermometer hitting 97 degrees during the 1909 race that came to be known as "The Inferno" and the 1976 "Run for the Hoses" that started in 100-degree heat and finished with spectators sprinkling winner Jack Fultz with garden hoses to cool him down.
Hopkinton residents Ted and Nanda Barker-Hook have been handing out sports drinks, coffee, water, bananas and sunscreen on the road leading to the starting gate for the past five years.
This year, no one was touching the coffee.
Those who did show up said they are prepared.
"You've got to know your own body," Mike Buenting, of Minneapolis, who has run 10 marathons, said as he waited for the starting gun. "You have to know how to hydrate, and the rest will take care of itself."