Eva Risztov of Hungary held on to win the gold medal for the women's marathon swim at the London Olympics after a desperate sprint finish to the 10km race.
American Haley Anderson won the silver medal after making a late charge to catch Risztov, while Italy's Martina Grimaldi won the bronze on Thursday.
Britain's Keri-Anne Payne, who won the gruelling event at the past two world championships, finished fourth from the 25 starters at the Serpentine, a recreational lake in Hyde Park.
A former Olympic pool swimmer, who quit the sport in 2005 then made a comeback in open water in 2009, Risztov led for all but one of the six loops the competitors were required to swim, Reuters reports.
She opened up a gap on the leading pack at the start of the final loop and was three body lengths clear approaching the finish when Anderson started to reel her in.
Anderson drew level with Risztov as they approached the finish, but the Hungarian kicked again and got her hands on the pads first in 1 hour 57min and 38.2s - just four tenths of a second in front of Anderson.
Grimaldi, runner-up at last year's world championships in Shanghai, won the bronze medal.
The exhausting race took its toll on South Africa's Jessica Roux and Brazil's Poliana Okimoto, who were both hauled from the water before the end.
