The 112th Boston Marathon got started Monday with defending champion Robert Cheruiyot and a field of more than 25,000 runners leaving the starting line in Hopkinton for the 26.2-mile run to Copley Square.

Cheruiyot was looking for his fourth Boston win. Lidiya Grigoryeva, last year's women's winner, was also trying for a repeat.

South African Ernst Van Dyk led from start to finish in the men's wheelchair race of the Boston Marathon to win for the seventh time in 1 hour, 26 minutes, 49 seconds. It was the second slowest time in his seven victories. He won by a huge margin. No one was near him when he crossed the finish line on Boylston Street.

The marathon comes a day after the U.S. Olympic women's trials featured the top American runners fighting for a berth in the Beijing Game. Deena Kastor, Magdalena Lewy Boulet and Blake Russell finished in the top three to earn a chance to run in the Olympics. They served as grand marshals for Monday's race.

Also in Monday's field was seven-time Tour de France winner Lance Armstrong.

The second-largest field in the race's history gathered in Hopkinton under an overcast sky and temperatures around 50 degrees. The wheelchair racers left first, at 9:26 a.m., followed by the elite women at 9:35 and the elite men along with the main field at 10:00.

Some tried to quell their nerves by having a bite to eat and relaxing in the athlete's tent near the starting line in Hopkinton. Two dozen runners from Korea, however, danced to loud drum music in front of a church, their bodies wrapped in multicolor sashes.

Sunny-Kim, a church elder, said the dance should help the runners, who traveled from Korea to run for charity, get excited for the 26.2 miles ahead of them.

Wendy Terris didn't need any help.

The 38-year-old runner from Milwaukie, Ore., ran the U.S. Olympic trials in 2 hours, 55 minutes, 28 seconds on Sunday and then planned to run her second marathon in two days.

"I'm in town anyway, and I'd just rather run than watch," she said. "I'm a participant. I'm not very good at spectating."

Elite marathon runners usually compete twice a year, once in the fall season and once in the spring, but that's never been enough for Terris. She ran 17 marathons in 17 months in 2002-03 � including one streak of three in three weeks � while posting an average time of under 3 hours.

So running on back-to-back days didn't seem too daunting for her, although she did get a little harried finding the time to pick up both registration packets while attending the necessary meetings on Saturday.

Winners of the men's and women's elite divisions will each receive guaranteed prize money of $150,000 � a record level in the majors, which include London, Chicago, Berlin and New York City. A fourth victory for Cheruiyot would put him alongside "Boston Billy" Rodgers and seven-time winner Clarence DeMar in the race's record books.

"A marathon is the hardest thing in life," said Cheruiyot, who gave Kenya its 15th men's title in 17 years. "To win four times, you have to be a disciplined man. You have to know what you want in life."

The overall purse of $796,000 is the richest of the World Marathon Majors events.

Before the race, Spyros Zagaris, mayor of Marathon, Greece, presented Hopkinton with a replica of a cup that was given to the winner of the first modern Olympic marathon in Athens in 1896. He vowed to build strong ties between his city and Hopkinton, both homes of the start of famous marathons.