Defending champions United States produced an extra-time winner to claim Olympic gold after a 1-0 win over Brazil in the women's football tournament on Thursday.

The Americans replicated their extra-time triumph over the Brazilians in the Athens Olympics final four years ago to deny the South Americans yet again.

It was a courageous effort by the United States, who for long periods absorbed tremendous pressure from the Brazilians, spearheaded by their lethal strike pair of Marta and Cristiane to win it in the first period of extra time.

Midfielder Carli Lloyd proved America's hero with a rasping angled drive that eluded the despairing dive of Brazilian goalkeeper Barbara in the 96th minute. The two great rivals produced a classic encounter, full of fierce physical contests and high levels of skill thrilling the capacity crowd at the Workers Stadium.

The Americans are rebuilding after a fractious campaign at last year's World Cup in China where they were taken apart by Brazil 4-0 in the semi-finals and finished with the bronze behind champions Germany.

In a breathless opening 45 minutes, US goalkeeper Hope Solo courageously saved at Cristiane's feet in the 31st minute.

Two-time world player of the year Marta thrilled the capacity crowd with her electrifying running, wriggling her way around two defenders but fired just wide three minutes later.

USA right-back Heather Mitts was yellow carded for bringing down midfielder Formiga in full flight and minutes later it was the dangerous Marta again, this time swinging in a high free kick which Solo did well to hold under pressure.

Nearing halftime Marta again darted clear but her cross to Cristiane was put behind for a corner by defender Lori Chalupny.