By Angus MacSwan and Amy Tennery

RIO DE JANEIRO (Reuters) - In a spectacular final day of the Olympic rowing regatta on Saturday, the United States reasserted their extraordinary dominance in the women’s eight, powering home to a third consecutive gold.

In the men’s eight, Britain overcame defending champions Germany, a result that put Britain on top of the rowing medals table with three golds.

But while the Americans extended their unbeaten run, the most thrilling race on the sun-dappled Rodrigo de Freitas Lagoon was the men’s single sculls.

In an incredible finish, Mahe Drysdale of New Zealand and Croatia's Damir Martin crossed the line at the same time as Martin appeared to pull past the defending champion. With the two rowers asking each other who had won, the gold was eventually awarded to Drysdale by a photo finish.

“It was an agonizing wait,” said Drysdale, who collected his second gold and third medal in the event.

In the day’s fourth final, favorite Kimberley Brennan of Australia comfortably won the women's single sculls, leading from the start to add the gold to the bronze she claimed in London.

Bruce Springsteen’s “Born in the USA” blared from the lead speakers after the U.S. women's eight team crossed the finish line, winning the United States’ only gold in the regatta.

Under coach Tom Terhaar, the United States have won 10 consecutive world titles in the event.

It was a second Olympic gold for Meghan Musnicki and Elle Logan, the only two members of the crew who competed in the London 2012 Games.

The United States took the lead in the third section after Canada and the Netherlands made the early running. The British team came good in the last stretch to claim silver and Romania made a late surge to take bronze.

The grand finale of the regatta, the men’s eight was always going to be a battle of attrition as a win by either Britain or Germany would also decide who topped the medal table.

While Germany were favorites, Britain have beaten them in the last three world championships. They led all the way, even though the Germans closed the gap toward the end.

The Netherlands took bronze.

Britain's Pete Reed paid tribute to the German and Dutch crews.

"It's just been a massive fight, not just in the last couple of hours, it's been going on for months and years and years. It's easy to say now but we like all these guys personally but on the water we're the biggest of rivals. We fight tooth and nail, it's just been the hardest battle for a long time," he said.

The men’s single sculls had been billed as a duel between the 37-year-old New Zealander Drysdale and his friend and arch rival, the Czech Ondrej Synek. But Martin took an early lead, chased by Drysdale and Synek. The Kiwi moved ahead coming into the last section but with a last lunge Martin appeared to have edged it.

"I was feeling quite comfortable, sitting out in front, then Damir started lifting the rate and I realized he was becoming quite a big threat so I tried to chuck in some strokes," Drysdale said. "He kept closing the gap”.

“I was fortunate enough to have the boat just surging through the line at the right time”.

Martin accepted the defeat with grace.

“I gave 1000 percent of myself,” he said. “I am more satisfied with a good race than a silver medal. The next one is going to be another color."

Drysdale's gold was the second for the New Zealand team and they finished third in the table behind Britain and Germany.

The only surprise in the women’s sculls was the fourth place for New Zealand's Emma Twigg in what had been seen beforehand as an Antipodean duel. The United States' Gevvie Stone took silver behind Brennan and China’s Jingli Duan claimed bronze

Brennan has dominated the class since taking bronze at the 2012 London Olympics, but her regatta got off to a rocky start when she sank nearly sank in rough conditions last Saturday and she came in 14th in the heat rankings.

High winds had forced two days of racing to be called off earlier in the week. There had also been concern in the run-up to the Games about pollution in the lake, but this turned out not to be a problem.

(Reporting by Angus MacSwan and Amy Tennery; Editing Meredith Mazzilli)