LONDON (CNN) -- With just two days left of the London 2012 Games, the finest sprinters of Team USA and Jamaica's champions Usain Bolt and Yohan Blake are readying for a final showdown in the men's 4x100-meter relay.
The Jamaican quartet is the odds-on favorite as it seeks to keep the title it won in Beijing and earn a sixth gold medal for Bolt, who has already made history by defending both his 100-meter and 200-meter titles.
Team USA ran a national record of 37.38 to qualify for the final, a fraction of a second faster than Jamaica.
The Americans will hope to follow the lead of the U.S. women's 4x100-meter team, which won gold Friday and set a new world record in the process.
Team GB failed to make Saturday's relay final after botching a baton handover, so the home crowd's hopes of gold on the last night of competition in the Olympic Stadium rest on the shoulders of endurance runner Mo Farah.
If the 5,000-meter world champion manages a gold in that event he will double his medal haul from this Games, following his win in the 10,000-meter race a week ago.
Meanwhile, South Africa's Caster Semenya, the athlete at the center of a gender row three years ago, goes into the women's 800-meter final among the favorites after posting the fastest time in the semifinals. Kenya's Pamela Jelimo, the defending champion, and Russia's Mariya Savinova are also in contention for a medal.
The women's 4 x 400-meter relay final will again pit Jamaica against the United States, although Russia and Great Britain also posted fast qualifying times.
With 32 gold medals up for grabs across 15 sports, it's set to be a busy day outside the stadium, too.
The first medal for Team USA came in the women's mountain bike competition at Hadleigh Farm in Essex, with a bronze for Georgia Gould of Baltimore. Gold went to France's Julie Bresset and silver to Sabine Spitz from Germany. The venue, which made its Olympic debut Saturday, hosts the men's mountain bike event Sunday.
The U.S. women's basketball team will shoot for five straight Olympic gold medals when it goes up against France later Saturday.
The French can't claim the healthy winning margins of the Americans, nor can they boast the likes of Diana Taurasi, Candace Parker or Maya Moore. But they are no slouches either, having won each of their seven contests so far this Olympic Games.
Team USA's women's volleyball squad is also guaranteed a gold or silver in the final against Brazil. Japan beat South Korea to take the bronze.
Brazil, the host of the next summer Games in 2016 and a famously soccer-mad nation, had hoped for its first Olympic football gold in the men's final at Wembley but instead saw Mexico claim a convincing 2-1 victory.
The Brazilians got off to an inauspicious start when they conceded a goal by Mexico's Oribe Peralta in the first minute of the game. Peralta headed the ball in for a crucial second goal with 75 minutes gone.
Brazil came back with a goal in the 90th minute but failed to capitalize on a chance in the final seconds, giving gold to Mexico.
A gold for Russia came in the men's 50-kilometer race walk, which set off on The Mall by Buckingham Palace on Saturday morning.
Just over three-and-a-half hours later, Sergey Kirdyapkin crossed the line first to take gold, ahead of Australian Jared Tallent, who took silver in Beijing.
The field was without Beijing gold-medalist Alex Schwazer, who was expelled from the Games on Friday after testing positive for a banned substance, recombinant erythropoietin (rhEPO), which aids red blood cell production. The 27-year-old Italian had set an Olympic record four years ago, but it was beaten by Kirdyapkin on Saturday.
Another athlete, Syrian hurdler Ghfran Almouhamad, was disqualified from the Games Saturday, the International Olympic Committee said.
Almouhamad, who went out in the heats of the women's 400-meter hurdles, tested positive for the banned substance methylhexaneamine, a stimulant.
Over at the Aquatics Center, China's 19-year-old diver Qiu Bo enters the 10-meter final as the runaway favorite, as the top qualifier and recipient of a remarkable 25 perfect 10s in last year's FINA/Midea Diving World Series 10-meter event.
Challenging him for the top spot Saturday night will be countryman Lin Yue, Team USA's David Boudia -- who placed second in the World Championships last year -- and Germany's Martin Wolfram, among others. Team GB's Tom Daley hopes to live up to the home crowd's expectations after placing fourth in the semifinal.
Team GB's first gold medal of the day came on the sparkling waters of Eton Dorney Lake, when Ed McKeever won the men's K1 200-meter canoe sprint.
The gold was the 26th for the host nation, which is in third in the medal table, behind the United States and China but ahead of Russia.
Ukraine picked up gold in the men's C1 200-meter canoe
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