BOSTON (AP) – Robert Cheruiyot won the Boston Marathon for the third time Monday, defending his title in the remnants of a soaking nor’easter to bring Kenya its 15th victory in 17 years. Russia’s Lidiya Grigoryeva captured the women’s crown.

Mr. Cheruiyot, who also won in 2003, set the course record last year but fought the wind and rain to finish in a slower, unofficial time of 2 hours, 14 minutes, 13 seconds.

“When the lion is chasing the antelope, he doesn’t look back. He has to eat,” Mr. Cheruiyot said. “So when I run, I don’t stare at my time.”

Mr. Cheruiyot outkicked countryman James Kwambai as they headed into Kenmore Square with a mile to go and beat him by 20 seconds. The defending champion kept his feet under him as he crossed the finish line – something he had a bit of a problem with when he won in Chicago last fall.

That fell left him with a concussion and headaches that persisted until as recently as last month. This time, Mr. Cheruiyot held his arms to the side and blew a kiss to the crowd as he stepped over the slip-proof line 20 seconds ahead of Kwambai.

Ms. Grigoryeva, who set the course record in Los Angeles last year, veered to the stands to grab a Russian flag just before crossing the finish line to win by 40 seconds in 2:29:18. Top American hope Deena Kastor fell back after stomach problems diverted her from the course for a minute near the midpoint.

“It’s hard to deal with a disappointing performance when you’ve prepared for so much better than you did out there,” said Ms. Kastor, the defending London champion, American record-holder and Olympic bronze medalist.

The weather was milder than forecasters had feared – 52 degrees with a moderate rain at the start_ and the sun even came out halfway through. But winds picked up as the runners turned onto Beacon Street in Cleveland Circle for the last, long homestretch to Copley Square.

“From the waist down it was horrible,” said Peter Gilmore, who was the top American, in eighth place. “My legs froze. It was the cold, my hamstrings and everything just started cramping up. Once the moves started, especially at Heartbreak, that was it.”

The leading women ran in a pack of seven for the first half of the race before several, including defending champion Rita Jeptoo and Ms. Kastor, began to fall behind. Ms. Kastor fell back after the midpoint, and Jeptoo at the 17-mile mark, heading into the Newton hills.

Ms. Grigoryeva, Latvia’s Jelena Prokopcuka and Mexico’s Madai Perez ran shoulder to shoulder from there until Ms. Perez and then Ms. Prokopcuka fell back as they crossed the Massachusetts Turnpike and headed into Kenmore Square.

The two-time defending champion of the New York City Marathon, Ms. Prokopcuka was second to Ms. Jeptoo in Boston last year in the closest finish – 10 seconds – in the history of the women’s race. This year’s race wasn’t as close but her finish was the same; Ms. Perez was third, another 18 seconds back.

Mr. Cheruiyot won in 2:07:14 last year and then went on to win Chicago. But what seemed to be a runaway turned scary when he slipped on the finish line and banged his head on the pavement as he raised his hands to celebrate breaking the tape.

Although at first it wasn’t even clear he made it to the end, his torso bounced across the line as he fell and hit his head. Since then, he’s had trouble sleeping, blurry vision and back problems. During a training race three weeks ago he went back to the hospital because of headaches.

Back in Boston, though, Mr. Cheruiyot managed to stay upright on the slick and puddled pavement.

A total of 23,903 runners registered for the race, with 2,449 choosing not to pick up their bib numbers over the weekend. More no-shows were expected at the start, and organizers worked through the night to line up shelters for those dropping out along the course.

Pumps have been stationed at low-lying areas in case of flooding. Ponchos were provided for workers assigned outdoors. Runners were warned by e-mail to wear appropriate clothing.

Near the start in Hopkinton, the usual carnival atmosphere was subdued. The town green was nearly empty less than two hours before start time, with few hot dog stands and no lines at the portable restrooms. A vendor who ran out of ponchos Sunday was selling trash bags for $1 apiece.

One reason may be the new starting time – 10 a.m. for the main field, after more than 100 years of noon starts – that was adopted in part, ironically, because of a few years of afternoon heat. The earlier start also allowed cities and towns along the route to have their roads back sooner.

Many runners started in jackets and gloves but ditched them as they warmed up over the day. By the time the lead pack of seven women reached Natick after about 10 miles, the rain had stopped and the wind had died.

Jeptoo struggled to remove her overshirt as they went through Wellesley, running a few yards with it stuck on her head. Kastor ditched her sleeves as well.

Despite a disappointing finish, Ms. Kastor earned the American title and a bonus of $25,000. She has said she does not want to run the marathon at the worlds in Osaka, Japan.

Mr. Cheruiyot is in line for a nice little bonus of his own: He all but wrapped up a $500,000 bonuses from the World Marathon Majors circuit; Jelena Prokopcuka leads the women’s points race with 55 points (25 points are awarded for a win, 15 for second).

The bonuses will be paid to the top men and women after the world championships in Osaka and fall marathons in Berlin, Chicago and New York.