LONDON -- Usain Bolt, undefeated and unparalleled as an Olympian, whisked Jamaica’s 400-meter relay team to the once-unthinkable world-record time of 36.84 seconds in his London finale.

Bolt won his third gold medal of his second Olympics to go with the three he won four years ago in Beijing. Call it a double-triple, or unprecedented. In Olympic finals, he is 6-0 and has set four world records.

In the last 100 meters of the last event on the Olympic Stadium track Saturday night, Bolt and American Ryan Bailey grasped their batons almost simultaneously as they took off down the home stretch. Within three strides, Bolt was blasting into the lead. Spectators rose as they kept an eye on the clock. Bolt looked light on his long legs, but he was pushing hard and gritting his teeth when he leaned across the line — for a change. He saw the time and knew he had delivered.

“A wonderful end to a wonderful week,” he said. “What else do I need to do to prove myself as a legend?”

Over a span of seven days, three finals and 38 seconds, Bolt accomplished everything he had promised in his quest to become “a living legend,” and it wasn’t close. But when he asked an official if he could keep the yellow baton as a memento, he was told no, or he would be disqualified. Bolt handed it over, got it back later as he bowed to the official and had it autographed by his teammates.

“I like to break barriers,” he said. “It sets you off from other people.”

On a night of multiple medal-winning, Sanya Richards-Ross won her second gold, running the last leg of the 1,600-meter relay with the same smooth strength she showed in the open 400 meters. The United States finished in 3:16.87, almost four seconds ahead of Russia in second and Jamaica in third.

“Two golds — that’s what I’ve always dreamed of,” said Richards-Ross, a graduate of St. Thomas Aquinas in Fort Lauderdale. “I call it the sprinkles, because winning the 400 was my cake and icing.”

“I felt like I was running a victory lap they gave me such a big lead,” added Richards-Ross, whose dynamic comeback leg in 2008 enabled the U.S. to beat Russia. “It was nice to be able to prance around the track one more time.”

Allyson Felix, who ran the fastest split of the field on her 47.8-second leg, won her third gold, the first U.S. woman to do so since Florence Griffith-Joyner in 1988.

Felix won each at a different distance — the open 200, the 400 relay and the 1,600 relay.

Great Britain’s Mo Farah added a gold in the 5,000 meters a week after winning the 10,000.

“My wife is expecting twins, and I didn’t want to have a gold medal for one and the other was left out,” Farah said.

Farah was patient during the first two-thirds of a tactical, nerve-racking race.

He moved to the front with two laps to go, then held on as first Kenya’s Thomas Longosiwa and then Ethiopia’s Dejen Gebremeskel challenged him.

Even after racing 12 miles in his events, he had enough left to kick through a 52.94-second last lap. He kissed his hands and slapped his bald head as he crossed the line, and 80,000 spectators roared at maximum volume for the Somali-born, London-raised Farah.

His time of 13:41.66 was the slowest winning time since 1968.