American Sanya Richards-Ross won the women’s 400m Olympic title on Sunday in a time of 49.55sec to end a 28-year gold drought in the event for the United States.

Defending champion Christine Ohuruogu of Great Britain finished second in 49.70sec while DeeDee Trotter of the United States took bronze in 49.72sec.

Richards-Ross, 27, became the first American to win the Olympic title since Valerie Brisco-Hooks in Los Angeles in 1984 and will attempt to emulate her when she tries to add 200 metres gold later in the Games.

“This win is impossible to describe,” said Richards-Ross, who has the chance of leaving with three golds as she will also go in the 4x400m relay.

“I worked so hard for that and I prepared for this moment over and over for the last four years.

“I just fought all the way to the end. There have been some very tough times in my life but this truly is a magical one that makes the painful memories recede,” added the Jamaican-born star.

Five years ago she almost had to retire because of a mystery illness initially diagnosed as Behcets syndrome but which a new doctor believes is a skin disease.

In a thrilling race, Richards-Ross came strongly off the bend to fight it out with Trotter while Ohuruogu finished with a stunning final burst.

However, unlike in Beijing four years ago it was not enough to see the Briton - who lives near the Olympic Park - to get past the 2009 world champion.

Richards-Ross, who is married to NFL defensive back Aaron Ross, shook her hands in celebration after crossing the line on realising she had gained revenge on her bitter rival for defeat four years ago.

Ohuruogu, also world champion in 2007, was distraught at the end because of the race she had run, although she graciously did a lap of honour.

“I was stunned,” she said. “I was heartbroken actually ... to lose your title like that.

“It was tough but Sanya is a worthy competitor and she ran a good race so I have to be happy with what I did. I could have been last.”