Bolt does the business

Jamaican sprint star Usain Bolt silenced his critics with a dominant win in the 100m Olympic final. (AAP)

Jamaican sprint star Usain Bolt silenced his critics with a dominant win in the 100m Olympic final. (AAP)

Usain Bolt defied the doubters to win the 100m gold medal, while Ben Ainslie has become the most successful Olympic sailor of all.

He had his doubters, but Usain Bolt always knew he was going to create history.

The fastest man ever beat the fastest field ever to become the first man since Carl Lewis in 1988 to successfully defend the Olympic 100m title in London on Sunday night.

"I knew it was going to be like this," said Bolt.

"There wasn't a doubt in my mind that it was going to be loud and it was going to be great and you can feel that energy."

After a conservative start, Bolt hauled the field in and then stormed home alone to win in 9.63 seconds with his fellow Jamaican Yohan Blake second in 9.75 and American Justin Gatlin third in 9.79 as the the first seven finishers all ran under 10 seconds.

It was the second quickest time in history, behind Bolt's own world record of 9.58.

"When it comes to business I do what I have to do. I have a great talent," Bolt said.

After being disqualified for a false start in last year's world championships, being beaten by Blake in the 100m and 200m at the Jamaican trials and hints of a hamstring injury, Bolt performed when it mattered in front of a full house of 80,000 at the Olympic Stadium.

"I've said it from the start, people can talk, all they can do is talk," the 25-year-old said.

"I tell you people that when it comes to the championships it's all about business to me and I brought it."

While Bolt confirmed his place as the greatest sprinter of all, Britain's Ben Ainslie won his fourth straight gold medal and fifth medal overall, making him the most successful sailor in Olympic history.

Ainslie had trailled the Finn class for most of the Games regatta in Weymouth Bay, but pulled off a remarkable win when he came ninth in Sunday's final race to overtake Denmark's Jonas Hogh-Christensen who gave up the gold medal position after finishing the race last.

He eclipses Denmark's Paul Elvstrom as the most successful sailing Olympian. Elvstrom won four straight gold medals from 1948-60, including three in the Finn class.

Andy Murray continued Britain's golden Games on Sunday, beating world No.1 Roger Federer for the men's singles tennis gold at Wimbledon, reversing the result from the Wimbledon final last month.

Murray dominated a listless Federer 6-2 6-1 6-4.

"It was the biggest win of my life," said an emotional Murray. "I've had a lot of tough losses in my career. This is the best way to come back from the Wimbledon final. I'll never forget it."

But the Scotsman couldn't add a second gold when he and Laura Robson took silver after losing the mixed doubles final to Belarussian pair Max Mirnyi and Victoria Azarenka 2-6 6-3 10-8.

Serena and Venus Williams won the women's doubles gold for the US, beating Andrea Hlavackova and Lucie Hradecka of the Czech Republic in straight sets.

The day started with the women's marathon which was won by Ethiopian Tiki Gelana, while Kenya's Ezekiel Kemboi won the 3000m steeplechase and America's Sanya Richards-Ross took the 400m gold.

China completed the first clean-sweep of all five badminton gold medals when it won the men's singles and doubles finals and is also heading toward an unprecedented haul of all eight diving titles after Wu Minxia won the women's 3m springboard.

China's five gold medals on Sunday took it back to the top of the medals table with 30 golds to 28 for the US, with Britain in third with 16.

History was also made by the first women boxers to compete in the Olympics, with Russia's Elena Savelyeva beating North Korea's Kim Hye-Song in the debut bout.