The crowds packing the main stadium on Saturday night erupted in wild cheers as Bolt took the baton from Yohan Blake and ran across the finish line to help Jamaica to victory in a record 36.84 seconds in the 4x100-meter relay. He added that gold to the ones he earned in the 100 and 200.
The United States got the silver in 37.04, matching the old record that Bolt helped set at last year's world championships. Trinidad & Tobago took the bronze in 38.12 after Canada, which was third across the line, was disqualified for running outside its lane.
Bolt's latest victory makes him the first person to win golds in the 100 and 200 metres and the 4x100-meter relay at consecutive Olympic games. But while he won all three with world-record times in Beijing, his victories in the two individual sprints in London were outside the world marks he set in 2009.
Bolt's victory followed that of Briton Mo Farah, who added a second Olympic gold to his collection, winning the 5,000 metres as a frenzied home crowd cheered.
The Somali-born runner, who last Saturday gave Britain its third athletics medal of the night when he won the 10,000 metres, delighted the public by kissing the ground then doing a few situps. He ran a time of 13 minutes, 41.66 seconds. Dejen Gebremeskel of Ethiopia took silver and Thomas Longosiwa of Kenya collected bronze.
Moments later, Caster Semenya from South Africa managed a silver in her Olympic debut in the 800-meter race three years after being forced to undergo gender tests.
She was last for most of the race and sped up with 250 metres to go, but could not pass world champion Mariya Savinova of Russia, who took gold. Russia also took the bronze with Ekaterina Poistogova.
Savinova finished the race in a season's-best 1 minute, 56.19 seconds, beating Semenya by 1.04 seconds.
In what turned out to be a good night for Russia, Anna Chicherova took the gold medal in women's high jump.
Allyson Felix gave her 4x400 relay team a big lead halfway to give the Americans another gold — her third of the London Games after the 200 and 4x100 relay. Teammate Sanya Richards-Ross added this medal to her 400-meter gold.
In other medals Saturday, Russia swept the gold medals in race walking: Sergei Kirdyapkin of Russia won the men's 50-kilometre walk, breaking the Olympic record by more than a minute, and Elena Lashmanova of Russia in the 20-kilometre women's race in a world record.
Lashmanova overtook defending champion and fellow Russian Olga Kaniskina in the last meters of the race women's 20-kilometre race walk to win gold at the London Games and break the world record in the event.
The 20-year-old Lashmanova was behind her Russian teammate through the race that Kaniskina has lead until the finish line was within sight. Lashmanova stepped up and clocked 1 hour 25 minutes and 2 seconds, seven-seconds ahead before the three-time world champion Kaniskina.
Qieyang Shenjie of China claimed bronze. Qieyang is the first Tibetan athlete China has ever fielded in the Olympic Games. She finished 14 second behind the winner.
Mexico won its first gold of the games when Oribe Peralta scored after just 29 seconds and then added another in the second half to help his side beat Brazil 2-1, the country's first Olympic football title.
In other team sports, Brazil won a second straight Olympic gold medal in women's volleyball, Norway took a gold medal in women's team handball and Germany won a gold in men's field hockey.
Another Olympian known as the "Usain Bolt on Water" — British sprint kayaker Ed McKeever — won the first gold medal of 32 to be presented Saturday. McKeever won the inaugural 200-meter K-1 sprint event at Dorney Lake west of London.
In sailing, Tamara Echegoyen, Angela Pumariega and Sofia Toro of Spain won gold in women's match racing in the best-of-five final over Australia.
In other finals Saturday, Keshorn Walcott of Trinidad & Tobago won a gold medal in men's javelin, and David Svoboda of the Czech Republic took gold in men's modern pentathlon.
With the end of athletics Saturday, the stadium will make way for Sunday's closing ceremony. The early word is that the 80,000-seat venue will be transformed into a giant jukebox of British pop, with The Spice Girls and The Who among the acts set to perform.
In other Olympic news, a female Syrian athlete has been kicked out of the games for doping. The IOC said 400-meter hurdler Ghfran Almouhamad tested positive for the banned stimulant methylhexaneamine on Aug. 3. The backup "B'' sample confirmed the positive finding.
The 23-year-old athlete finished eighth and last in her first-round heat on Aug. 5.
And the IOC has told South Korean officials to bar a football player from collecting his bronze medal on Saturday after he displayed a flag with a political message at the third-place match against Japan.
The IOC said it has opened its own investigation into the South Korea national flag paraded after Friday's match. It carried a slogan supporting Korean sovereignty of islets which are disputed territory between it and Japan.