A freak collision ended the London Marathon hopes of leading contenders in two races.
Women's Olympic champion Tiki Gelana veered across the course at a drinks station after 15km.
However she ran straight into the path of wheelchair athlete Josh Cassidy who was powerless to avoid her.
The Canadian, who won the 2010 men's wheelchair race in London, removed his helmet and complained bitterly to officials - though he eventually continued.
Gelana was only briefly delayed but sustained a cut knee on falling, and could not keep up with the leading runners.
The men's wheelchair race was won by Australia's Kurt Fearnley, with Britain's Olympic champion David Weir finishing fifth.
American Tatyana McFadden won the women's wheelchair race, following up on her victory in the Boston Marathon last week.
Priscah Jeptoo of Kenya won the women's Marathon on her first attempt.
Runners in London observed a minute's silence at the start to pay tribute to victims of last Monday's Boston bombings.