Russia's Natalya Antyukh held off a late surge from current world champion Lashinda Demus to win Olympic gold in the women's 400m hurdles.
Antyukh ran a personal best of 52.70 seconds to win a second Olympic medal after claiming bronze in the 400m at Athens 2004.
"I'm not surprised by the winner but I am surprised by that time: 52.70 seconds. These ladies have arrived into this Olympic Games and are delivering great performances. Antyukh's technique is strong with good speed, but if she combined it with good hurdling rhythm she'd take chunks off her time."
Demus, bidding to become the first reigning 400m hurdles world champion to win Olympic gold, finished in 52.77.
Zuzana Hejnova claimed bronze for the Czech Republic in 53.38.
Demus made a blistering start but Antyukh, 31, hunted her down and led off the final bend.
The Russian stuttered over the final hurdle as Demus threatened to snatch victory, but held on to take gold on the line.
Her winning time was just 0.06 seconds outside the Olympic record set by Jamaica's Melaine Walker in Beijing four years ago.
"I am overwhelmed with emotion," said Antyukh. "I cannot believe what has happened. I need time for it to sink in.
"I cannot remember in detail how the race unfolded. It was a tough fight."
Denisa Rosolova, who was
reinstated to deny Great Britain's Perri Shakes-Drayton a place
in the final, finished seventh.