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South Africa's rowers pipped Britain and defending champion Denmark to gold in a thrilling lightweight coxless fours race on Thursday.

South Africa's James Thompson, Matthew Brittain, John Smith and Sizwe Ndlovu, world silver medalists, completed the 2km course in six minutes, 2.84 seconds.

"I kept my head down in the boat, we kept ourselves for the big sprint. They say that big sprinters finish second - not today," Smith said.

"We have had amazing support here. In South Africa, our Facebook has been going crazy."

The British team of Peter Chambers, Rob Williams, Richard Chambers and Chris Bartley put in a strong finish but wavered at the last to claim the silver in 6:03.09.

"We came to win, but it's an incredibly tight event. You can't take anything for granted," Williams said.

"The crowd are fantastic. That last 200 metres would have been a lot harder if they hadn't been there."

Denmark, going for its fourth Olympic title, had to settle for bronze after leading for most of the race, in 6:03.09, its quartet of Kasper Winther, Morten Jorgensen, Jacob Barsoe and Eskild Ebbesen, suffering fatigue in the final strokes.