Britain's Mo Farah completed a historic Olympic distance double double with victory in the 5,000m as American runner Matt Centrowitz scored an upset win to claim gold in the 1,500m.

Farah became the first man since Finnish great Lasse Viren in 1976 to retain two Olympic distance titles after storming to victory, a week after defending his 10,000m crown at Rio's Olympic Stadium.

The 33-year-old Somali-born Londoner once again produced a superb tactical race to outfox his rivals and take gold in 13min 03.30sec.

"Oh my God I can't believe it!" said Farah. "My legs were tired after the 10,000m and people had to bring me food in my room.

"This is the most satisfying win of the four, it is incredible.

"If you have dreams they can come true and I always wanted to achieve these for my kids because for so much of the year you don't see them. You want to show them something or rather the reason for the absences."

Centrowitz meanwhile produced the biggest upset on the final night of track competition, beating defending champion Taoufik Makhloufi of Algeria into second place to win gold in 3min 50.00sec.

Centrowitz became the first American man in more than a century to win the event, which has been shared exclusively between African runners since 1996.

The last American to win the 1500m in the Olympics was Mel Sheppard in the 1908 London Games.

"There's nothing like it. It doesn't compare to anything else I've won in my life," said Centrowitz.

"Doing my victory lap, I literally kept screaming to everyone I know 'Are you kidding me?'"

New Zealand's Nicholas Willis took the bronze medal in 3:50.24.

Centrowitz's win was one of three golds won by the United States, who also took both the 4x400m relays.

Golden finish for Felix

US track and field's golden girl Allyson Felix led home her team in the women's 4x400m, crossing the line in 3min 19.06sec to claim a record sixth gold medal.

The win maintains the USA's 20-year unbeaten reign in the event, which they have not lost since 1992.

Felix, who 24 hours earlier had helped the USA win 4x100m relay gold, has now won more track gold medals than any other woman athlete in history.

In the men's 4x400m, former Olympic 400m champion LaShwan Merritt led the US team home in 2:57.30 with Jamaica finishing in silver and defending champion the Bahamas bronze in 2:58.49.

Elsewhere South Africa's Caster Semenya completed a convincing victory in the 800m to win her first Olympic gold in 1:55.28.

Francine Niyonsaba of Burundi took silver in 1:56.49 with Kenya's Margaret Wambui claiming bronze in 1:56.89.

Semenya has been at the centre of a raging controversy in recent years because of her naturally occurring condition, hyperandrogenism, which causes elevated testosterone levels.

She has dominated the event since a sports court last year judged that an International International Association of Athletics Federations (IAAF) regulation limiting competitive testosterone levels was unlawful.

Shortly before Saturday's final, IAAF chief Sebastian Coe said his body would seek to revisit the question with the Court of Arbitration for Sport.

"This is a very sensitive issue. We will take the case back to the Court of Arbitration and it will be a good case based on medical and scientific advice," Coe said.

The other big winner Saturday was Spain's veteran high jumper Ruth Beitia, who scored the biggest win of her 20-year career with a gold.

The 37-year-old became the oldest woman to win an Olympic jumping event after clearing 1.97m. Beitia won on countback from Mirela Demireva of Bulgaria and Blanka Vlasic of Croatia.

The javelin was won by Germany's Thomas Rohler with a throw of 90.30m. Kenya's reigning world champion Julius Yego won silver with 88.24m while defending Olympic champion Keshorn Walcott of Trinidad and Tobago claimed bronze with 85.83m.