Rutto, who recorded the fastest ever marathon debut when he clocked 2:05:50 in Chicago last year, was running stride for stride with compatriot Sammy Korir when he slipped and crashed into a barrier.

As he fell he brought down Korir as well and the pair, both obviously shaken, got to their feet slowly and gingerly resumed running.

Rutto quickly recaptured his rhythm and eased ahead of Korir, the second fastest men's marathoner in history after world record holder Kenyan Paul Tergat who missed this year's race because of a calf injury. He finished well ahead of Korir (2:06:48) with Morocco's world champion Jaouad Gharib taking third place in a personal best of 2:07:02.

"It feels great to be champion of London," said Rutto, who suffered cuts on his knees from the fall. "I thought I was stronger than Sammy but the rain wasn't good."

Korir added: "The fall at 35 km stopped me winning the race. I thought I could win but for that. I hurt my leg."

Twice New York champion Margaret Okayo overhauled Romanian Constantuba Tomescu-Dita shortly after the 30-km mark to win the women's marathon in 2:22:35. Okayo has already been selected to represent Kenya at the Athens Olympics in August.

"I'm freezing wet but it's nice," Okayo told BBC television. "I hope Athens will be better for me because it's warm and my body likes warmth."

ABERA WITHDRAWS

In the men's race, which started 40 minutes after the women's event, a leading group of 18, headed by a trio of pacemakers, were still bunched at Tower Bridge, passing the halfway mark in 63 minutes 10 seconds

After 25 km of the 42.195-km race, Rutto, Korir and Tanzanian John Yuda broke away with Rutto setting an increasingly fierce pace before his fall.

Defending champion Gezahegne Abera, who failed to finish at last year's Paris world championships, dropped out before the 10-km mark. Limping heavily, the Olympic gold medallist walked off the course with what appeared to be a recurrence of the left Achilles tendon injury which forced him out of the Paris race.

The diminutive Okayo, 27, who was nicknamed "Cat" as a child because of her size, set the early pace, taking over from the designated pacemaker Liz Yelling of Britain soon after the start in Greenwich.

Running in a black woollen hat and black gloves, the 1.50 metres tall Okayo quickly stretched her lead to 90 metres ahead of Yelling after only five km.

She was still well ahead at 10 km but then began to lose her rhythm following her fast early pace and Tomescu-Dita seized the opportunity to take the lead five km later.

Tomescu-Dita passed the halfway stage of the race near Tower Bridge in 69 minutes 28 seconds then she in turn started to labour and Okayo began to draw closer.

Okayo held on to win with Russian Lyudmila Petrova overtaking the tiring Tomescu-Dita for second place in 2:26:02. Tomescu-Dita finished third in 2:26:57.

Pre-race favourite Gete Wami of Ethiopia, a former world 10,000 metres gold medallist, dropped out of the race with hamstring problems.