Helen Jenkins broke clear of the pack in style to win the women's Hyde Park triathlon and meet GB's selection criteria for the 2012 Olympics.
The Welsh 27-year-old struck out for the front as the running finale began and finished seven seconds clear of second-placed American Gwen Jorgensen.
"That hurt so much. I just kept running and running," said Jenkins.
Hyde Park forms one of triathlon's seven-leg World Championship Series, with the finale in Beijing next month.
Racing in the comparative cool of Saturday morning, the 67-strong women's field headed out of the park and on to the streets of London for the first time, replicating the expected London 2012 Olympic course.
This race served as the Olympic test event but, more importantly for the athletes, results here counted towards both this year's World Championship Series - a seven-race battle for the world title - and, for many nations, Olympic qualification.
Jenkins' gold medal, in a time of two hours and 34 seconds, was her third successive Hyde Park podium finish and her first-ever World Championship Series win.
"Normally when you win you're like, 'Ah yeah, it's easy,' but that hurt," she said.
"I didn't feel great on the swim, and on the bike I just tried to follow [British team-mate] Kerry Lang and stay safe.
"The run hurt, but I was at the front so I kept running and running. Someone said I had a gap so I thought I'd better keep pushing on - I kept pushing right to the end."
The result, in conjunction with her second-place finish in Kitzbuhel earlier this year, ensures she meets British Triathlon's selection criteria for the Games.
While that does not guarantee her selection next year, as others may yet qualify alongside her and force the selectors to choose between them, it moves Jenkins - who finished 21st at the Beijing Games in 2008 - closer to her second Olympic appearance.
Jodie Stimpson, who kept up with Jenkins for a time, led the other members of the British contingent over the finish line in 14th place. Vicky Holland crossed the line in 17th, Non Stanford was 38th and Kerry Lang came 51st.
Chile's Barbara Riveros Diaz, who led the World Championship Series coming into this race, struggled in the swim and finished 12th.
Canadian rising star Paula Findlay - hampered for some weeks by a hip injury - placed 29th.
Diaz still leads the overall series rankings, with Jenkins now up to fourth behind Findlay.
The men's race in Hyde Park begins at 1300 BST on Sunday and stars British brothers Alistair and Jonathan Brownlee, who can similarly meet the GB selection criteria for 2012 if they finish on the podium.
Alistair Brownlee won the London leg on his way to the world title in 2009 and comes into Sunday's race as the recently crowned European champion for a second successive year, but collapsed on the Hyde Park finish line in 2010 as Spanish rival Javier Gomez won.
Other Britons set to tackle the 1500m swim, 40km bike ride and 10km run include Tim Don and Will Clarke.
The World Championship Series moves to Lausanne, Switzerland, on 20-21 August before the series' grand final in Beijing on 10-11 September.