Romania's Sandra Izbasa exploited an error by American favourite McKayla Maroney to claim the Olympic gold medal in the women's vault final on Sunday.
The reigning world champion, 16-year-old Maroney produced an outstanding opening vault but then sat down on her landing on her second attempt, allowing Izbasa to snatch the title with a score of 15.191 points.
Maroney was left with the silver medal, while Russia's Maria Paseka came third.
It is Izbasa's second Olympic gymnastics gold, after her floor title in Beijing four years ago, and follows on from the bronze medal she won with Romania in the team final on Tuesday.
"I feel pretty good, but I know I have another final ahead," said Izbasa, who will also compete in the floor final.
"I can't say I feel fulfilled because I have the floor final ahead. It means a lot, but honestly I didn't expect it, especially as I was competing last in the final."
Germany's Janine Berger set the early pace with a pair of vaults that earned her a score of 15.016, before Canada's Elsabeth Black had to withdraw after hurting her left leg when she fell on her first vault.
Oksana Chusovitina moved into second place with a score of 14.783, but she was pushed into third when Paseka claimed the lead.
Maroney produced a huge Amanar vault worth 15.866 to stake a claim for gold but then disaster arrived on her second vault, as she sat down her landing before stalking from the mat in anger.
Her overall score of 15.083 took her up to first but she was immediately pipped by 22-year-old Izbasa, who produced two solid vaults to claim her second Olympic title and leave Maroney distraught.
"I know I can do better vaults, but I also know I didn't deserve the gold medal because I fell on my second vault," said the American.
"It happens. It's gymnastics. You can't always be perfect. Sometimes things don't go as planned."
Chusovitina's attempt to become the oldest female medallist in an individual Olympic gymnastics competition at the age of 37 ended in disappointment, meanwhile, as the German veteran finished fifth.
Romania's Sandra Raluca Izbasa competes during the women's vault final of the artistic gymnastics event of the London Olympic Games at the 02 North Greenwich Arena in London. Izbasa won the gold.