Yi Siling of China won the first gold medal of the London 2012 Olympics with victory in the women's 10m air rifle at the Royal Artillery Barracks.
The 23-year-old world number one and title favourite beat Poland's Sylwia Bogacka into second, with Yu Dan of China taking bronze.
Bogacka was leading until the eighth attempt of the 10-shot final when a wayward effort handed Yi first place.
Great Britain's Jennifer McIntosh was knocked out in the qualifying round.
McIntosh, who finished 36th out of 56 competitors in her first Olympics, said: "I'd have liked to be in the final, but performance-wise I felt like I handled it really well. You live and learn."
Yi and Bogacka reached the final with near-perfect scores of 399 out of 400, but Yi took the gold with an overall score of 502.9 to the Polish competitor's 502.2.
"It's very exciting," said Yi. "I have been up since five this morning. There was a lot of pressure on me. I'm very grateful to China and to my mother and father, who I love very much."
Defending champion Katerina Emmons of the Czech Republic was fourth.