Keri-Anne Payne won the women's 10km open water race in a sprint finish to give Great Britain their second gold of the 2009 Fina World Championships.
The 21-year-old Olympic silver medallist went one better in Rome as she finished first in a time of two hours, one minute and 37.1 seconds.
Russia's Ekatarina Seliverstova was one second behind in second, with Italy's Martina Grimaldi taking third spot.
Diver Tom Daley won Britain's first gold in the 10m platform on Tuesday.
The 10k race was billed as a straight head-to-head between Payne and eight-time world champion Larisa Ilchenko who beat the Manchester-based athlete by just over a second in Beijing last summer.
However, the Russian, who lost her 5km crown to Australian Melissa Gorman on Tuesday, pulled out midway through the race with a leg injury.
That paved the way for Payne, who only briefly lost the lead to Spain's Yurema Juarez Requena around the hour mark, to surge to victory in the Tyrrhenian Sea at the Ostia beach resort.
The big battle occurred behind the winner with Seliverstova pipping Grimaldi to silver in a photo finish.
I had not led all this way for nothing
Payne on BBC Radio 5 Live
Payne, who trains in Stockport, said she was determined not to finish second best again.
"When I was in the lead I put my head down and hoped nobody would pass me and they didn't," she told BBC Radio 5 Live.
"I had no idea where the Russian Ilchenko was. The Italian girl that came third caught up near the end, but I had not led all this way for nothing.
"I thought 'I won't be second best, I want to be world champion'."
Payne will now concentrate on her pool events - the individual medley over both 200m and 400m, with the first race on Sunday.
Meanwhile, German Thomas Lurz achieved a personal double by adding the men's 10km crown to the 5km title he won on Tuesday.
Andrew Gemmell of the United States finished second while his compatriot, Francis Crippen, came home in the bronze position.
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