Pre-race favourite Evans Rutto survived a fall and wet conditions to win his first London Marathon.
Rutto, who became the fastest debutant in marathon history in Chicago last year, broke away at 23 miles to finish in two hours six minutes 18 seconds.
Sammy Korir, who matched Rutto step-for-step until the Embankment, held on for second place, with world champion Jaouad Gharib in third.
Jon Brown was the first Briton home, well inside the Olympic qualifying mark.
Defending champion, Ethiopia's Gezahegne Abera, dropped out at the 10km mark with a recurrence of the Achilles tendon injury which forced him out of last summer's World Championships.
Rutto was running stride for stride with compatriot Korir when he slipped on the
cobblestones alongside the Tower of London and crashed into a barrier.
As he fell he brought down Korir as well and the pair, both shaken, got to their feet slowly.
But Rutto recaptured his rhythm first and and then pulled away from Korir, the second fastest man in marathon history.
"It feels great to be champion of London," said Rutto, who had cuts on his knees from the fall.
"I thought I was stronger than Sammy but the rain wasn't good."
Korir blamed the fall for losing the race. "I thought I could win but for that - I hurt my leg," he said.
The cold, windy conditions kept times slow, but Rutto, Korir and
Tanzanian John Yuda broke away from the pack at 25km with an injection of pace.
Yuda was dropped with six miles to go before Rutto kicked on to take his win.
Brown, running well within himself, ignored his pre-race row with London organisers over an appearance fee to finish in a time of 2:13.39.
Fellow Briton Dan Robinson also put himself into contention for the British Olympic squad when he clocked 2:13.56.