Sanya Richards-Ross breathed a sigh of relief when she won the women's Olympic 400 metres title at the third time of asking.
The American had 4x400 relay golds from the 2004 and 2008 Games but, until Sunday, no individual title.
"To come out here and be successful is my ultimate dream come true. It's a huge weight off my shoulders," Richards-Ross told reporters.
"I kept telling myself, 'You are the champion', but to go out there and accomplish it was really tough," added the 27-year-old who has overcome a series of health problems.
Richards-Ross, the most prolific sub-50 seconds female 400 runner, set off at a blistering pace but was behind Russian Antonina Krivoshapka and compatriot DeeDee Trotter coming off the final bend.
As her rivals visibly tired, Richards-Ross kept her form and, with a determined look on her face, reeled them in before breaking into a smile when she dipped for the line to win in 49.55 seconds.
Britain's defending champion Christine Ohuruogu was second and Trotter finished third.
"I got out really well, the first 50, I kind of backed off a little bit too much on the corner, I kept telling myself, 'Be patient', said Richards-Ross who had been favourite for the gold in Beijing four years ago but came third.
"I got to 100 metres and there were about four of us, which I'm not used to, so I kept saying, 'You can do it, you can do it'."
Ohuruogu came into the home straight in seventh but put on a late spurt to snatch the silver on the line by 0.02 seconds from Trotter in 49.70.
The crowd were urging Ohuruogu on but she had timed her run too late to take the spoils.
"I was heartbroken actually to lose a title like that," the 28-year-old said.
"It was tough but Sanya ran a good race. I'm happy with what I've done. It could have been worse. The line came too soon. I thought, 'It's gone, it's gone'."
Botswana's world champion Amantle Montsho finished fourth in 49.75.