Katie Ledecky, a 15-year-old from Bethesda, Md., upset the home crowd in London today by winning the Olympic gold medal in the women’s 800-meter freestyle race. Ledecky finished in 8:14.63, just fractions of a second short of the record held by Great Britain’s Rebecca Adlington, who took bronze.

Ledecky, a student at Stone Ridge School of the Sacred Heart in Bethesda, is the youngest ever to win the longest individual lap race in the Olympic women’s swimming program. She grabbed an early lead after the starting gun and for much of the race, seemed on the verge of breaking Adlington’s world record set in Beijing in 2008.

Mireia Belmonte Garcia of Spain took the silver medal.

Just before Ledecky’s win, Michael Phelps collected his 17th career gold medal by winning the men’s 100-meter freestyle. The race is widely expected to be the last individual race for the most accomplished competitor in the history of Olympic swimming. (Phelps, 27, has said he plans to retire after London.)

With Phelps’ and Ledecky’s wins, the United States raised its gold medal count to 21, 14 of which have come in the pool.

The races will be broadcast on NBC later tonight.