Sylwia Bogacka of Poland took the silver for her first major medal, and Yu Dan of China won the bronze.
Yi was the overwhelming favorite but it took a mistake from Bogacka in the eighth round of the 10-shot final for her to edge the unheralded Pole.
Bogacka shot a 9.7, her worst score of the final, and dropped to fourth. A near perfect score on her final shot gave her the silver ahead of Yu.
Yi finished with a score of 502.9 while Bogacka was at 502.2 and Yu at 501.5. Defending champion Katerina Emmons, who won a qualifying shootoff to make the final, finished fourth.