LONDON: Usain Bolt and his fellow Jamaicans could finish Saturday's last night of competition in the Olympic athletics stadium with a bang in a sprint metres relay shaping up as one of the fastest in history.

Before the biggest name in track and field takes centre stage again, however, Mo Farah's bid to add the 5,000m title to the 10,000 crown he won last weekend could give the host nation the perfect end to the meet.

Earlier in the day, at Wembley Stadium, Brazil play Mexico in the final of an Olympic soccer tournament that the five-times World Cup winners have amazingly never won.

The penultimate day of the London Games also sees five boxing finals, the women's basketball and volleyball finals, the men's and women's handball finals, and a men's hockey final between Germany and the Netherlands that should be a classic.

The sprint relay gives 100 and 200m champion Bolt the chance to break his first world record since 2009 and win his sixth sprint gold in two Olympics.

If Jamaica's relay squad need any more inspiration, they need look no further than the U.S. women's 4x100m quartet, who left their Jamaican rivals trailing on Friday and took more than half a second off a record set by East Germany in 1985.

The U.S. men look certain to push Jamaica all the way on Saturday after running 37.38 seconds in their semi-final, the third fastest time ever, while resting their two best racers.

Jamaica, resting Bolt, were only 0.01 seconds slower.

Farah is world champion in the 5,000m but looked tired in the heats and may find that challengers such as Ethiopians Dejen Gebremeskel and Hagos Gebrhiwet, Kenya's Isiah Kiplangat Koech and American Bernard Lagat have fresher legs.

DIBABA DENIED

Friday's women's 5,000 produced an upset as Meseret Defar surged to victory to deny her compatriot Tirunesh Dibaba, winner of the 10,000 a week ago, a historic second double of Olympic distance titles.

And the Bahamas, silver medallists four years ago, ran down a weakened U.S. 4x400m quartet in the home straight, ending the Americans' 28-year Olympic reign in the event.

The shadow of doping loomed larger over athletics than it has done at these Games as two former dopers won gold.

Asli Cakir Alptekin, who served a two-year ban for doping from 2004, led a Turkish 1-2 in the women's 1,500 metres, a distance riddled with drugs in recent years.

Russia's Tatyana Lysenko, who watched the 2008 Olympics on TV while serving a two-year doping ban, won the women's hammer.

And appearing in the men's 4x100m relay semi-finals were American Justin Gatlin and Briton Dwain Chambers, both time-served drugs cheats.

France and Kenya both confirmed pre-Games positive tests on distance runners Hassan Hirt and Mathew Kisorio, Kenya strongly denying Kisorio's allegations that blood-doping and steroid use were widespread in Kenya.

Saturday's men's 50km walk will be missing defending champion Alex Schwazer of Italy, excluded from the Games for using the blood-boosting erythropoietin (EPO).

In other events on the ninth day of athletics, Kenya's Pamela Jelimo defends her 800m title against world champion Mariya Savinova of Russia and South African Caster Semenya.

BRAZIL AT LAST?

Norway's Andreas Thorkildsen will be going for a third straight gold in the javelin against Czech Vitezslav Vesely, who has beaten him in all four of their meetings this year.

Russia's world champion Anna Chicherova is the favourite for the women's high jump, while the U.S., Russia and Jamaica are likely to share the medals in the women's 4x400 relay.

At Wembley, a Brazil side boasting Neymar, Oscar and the tournament's top scorer Leandro Damiao are under considerable pressure to live up to their status as favourites and improve on their silver medals of 1984 and 1988.

"I do feel under pressure, but it is no different to any other moment in these Olympic Games," said Brazil coach Mano Menezes.

"This is our third opportunity to win gold and we are going to take what we've learned from those two defeats and hopefully win on Saturday."

Their Mexican opponents, playing their first ever final, will be without injured playmaker Giovani dos Santos.

The women's basketball final sees France try to end a U.S. winning streak that stretches back to 1996.

"To beat the USA you have to do the perfect game. Perfect in defence, perfect in offence," said back-up point guard Edwige Lawson-Wade. "It's something that happens once every few years, but it happens. So anything is possible."

Germany defend their men's Olympic hockey title against their Dutch arch-rivals in a final that promises to be a classic between two physical, fast-paced, open, attacking sides with no clear favourites.

At the end of Friday's competitions, the United States led the overall medals table with 41 golds to China's 37 and host Britain's 25. AGENCIES