Christine Ohuruogu won Olympic 400m gold for Britain with a stunning surge down the home straight in Beijing.
The 24-year-old crossed the line in 49.62 seconds to eclipse Jamaica's Shericka Williams and American title favourite Sanya Richards.
Ohuruogu, who last summer completed a one-year ban for missing three out-of-competition drugs tests, added the Olympic crown to her world title.
The win makes Ohuruogu the first British female Olympic 400m champion.
"Everyone dreams about winning," said Ohuruogu, who sunk to the floor after her triumph. "But you never think it's a reality.
"I'm just so proud of myself. I crossed the line and just thought 'oh my goodness'.
"It's hard but my coach has always taught me you have to go into each race expecting to win."
Ohuruogu looked out of the race coming into the final bend but the Briton timed her race to perfection, just as she did in Osaka at the world championships last summer.
Richards, who went into the final as the overwhelming favourite after a dominant season, blasted out of the blocks but paid the price for the early pace.
As the American faded, Ohuruogu drew on her strength and pushed clear for the line to leave her rivals in her wake.
Williams took second in 49.69 secs with Richards settling for third in 49.93.
Two years ago, Ohuruogu's Olympic dreams were in tatters after she was handed a one-year ban for missing a trio of drugs tests.
Under British Olympic Association laws, any drugs offence results in an automatic lifetime ban from future Games.
OLYMPICS BLOGHowever, Ohuruogu successfully won an appeal last November because of "mitigating circumstances".
The Londoner was not at various training locations at specific times she had specified to testers and blamed a combination of 'forgetfulness" and last-minute venue changes.
Ohuruogu was born in Stratford, East London, just a few miles from the site for the London Games in 2012 and is tipped to be a star in four years' time, when her talented younger sister Victoria could also emerge as a challenger to her crown.
Ohuruogu's victory at the Bird's Nest stadium came just after Germaine Mason collected Britain's first athletics medal of the Games with silver in the high jump.
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