Eva Risztov of Hungary held on to win the gold medal for the women's marathon swim at the London Olympics on Thursday after a desperate sprint finish to the 10 kilometre race.
Haley Anderson of the United States won the silver medal after making a late charge to catch Risztov while Italy's Martina Grimaldi won the bronze.
Britain's Keri-Anne Payne, who won the gruelling event at the last two world championships, finished fourth from the 25 starters at the Serpentine, a recreational lake in Hyde Park that was constructed in 1730 and remains one of London's most iconic tourist destinations.
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.
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, whose older sister Alyssa won a gold medal at London as part of the American 4x200 metres freestyle relay team, drew level with Risztov as they approached the finish but the Hungarian kicked again and got her hands on the pads first in one hour 57 minutes and 38.2 seconds, 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 by the same tiny margin ahead of Payne.
The exhausting race took its toll on two competitors, South Africa's Jessica Roux and Brazil's Poliana Okimoto, who were both hauled from the water before the end.
Tens of thousands of people lined the banks of the lake on a glorious summer's day for one of the few events at the Games that were free for the public to watch.
They let out a mighty roar when the starter's gun was fired and the swimmers plunged from the pontoon into the murky water that they had to share with geese, ducks and swans, thrashing through thick weeds and poisonous algae that can cause severe skin rashes, eye irritation, vomiting and diarrhoea.