By Matt Falloon and Mike Collett-White
LONDON (Reuters) - Usain Bolt and Jamaica's speedsters smashed the 4x100 meters world record, Britain's Mo Farah brought London to its feet with another golden distance win and Mexico broke Brazilian soccer hearts in a thrilling penultimate day of Olympic action.
But Saturday's sporting highs were tempered by news that a Syrian runner was expelled from the Games for doping and a South Korean soccer player was barred from a medal ceremony for staging a political protest after a bronze playoff with Japan.
In a day brimming with golden opportunities - 32 titles were up for grabs - Bolt kissed off his one-man Olympic show to lead Jamaica home for gold in a blistering relay that brought London's track and field events to a shimmering close.
Bolt added that title to the 'double double' he won in the 100m and 200m, defending both after his Beijing triumphs and writing his way into Olympic history as one of the finest - and zaniest - sprinters the world has known.
As he crossed the line, Bolt cupped his hands in an 'M' shape above his head - a nod to Farah who had earlier run away from the pack to win the hosts' first men's 5,000m gold.
"It's always a beautiful feeling to end off like this," Bolt said. The quartet of Bolt, Yohan Blake, Michael Frater and Nesta Carter darted around the track in 36.84 seconds, beating their own record and leaving the United States trailing in their wake.
Farah, who snatched the 10,000m crown in London just days ago, is the seventh man to win both races at the same Olympics and the trailblazer of a British team that has claimed more medals than at any Games in more than a century.
"I wanted a gold medal for each of my two girls on the way," said the 29-year-old, whose wife Tania is heavily pregnant. "They could come any day now."
Russia's world champion Mariya Savinova saw off South African Caster Semenya to win the women's 800m, the U.S. triumphed in the women's 4x400m relay and Trinidad and Tobago's Keshorn Walcott struck a surprise gold in the javelin.
The final few moments of Olympic glory in track and field bring a close to an eventful penultimate day of the Games in which startling athletic prowess did not always dominate the headlines.
Syrian athlete Ghfran Almouhamad, who competed in the women's 400 meters hurdles, was the 11th athlete to be thrown out of the Games since the start of the Olympic period, which began on July 16, after testing positive for a banned substance.
The 10-strong Syrian team has attracted considerable media attention during London 2012, less for its sporting achievements than the bloody conflict raging at home between rebels and forces loyal to President Bashar al-Assad.
Politics also crashed the party when the International Olympic Committee (IOC) called for a South Korea soccer player to be banned from a medal ceremony after he held up a poster referring to his country's long-running territorial dispute with Japan - after the two teams had just battled for the bronze.
Five-time world champions Brazil's long quest for Olympic soccer gold continues after Mexico stunned the usually stylish South Americans with a 2-1 win.
Oribe Peralta put Mexico ahead after just 28 seconds and added their second in the 75th minute with a header before Hulk replied for Brazil in stoppage time in front of a London Games record crowd of 86,162 at Wembley Stadium.
The Brazilians, glittering with the considerable talents of Neymar, Hulk and Oscar, had been favorites for the title but failed to threaten a more direct and efficient Mexican side.
Brazil's women provided some consolation, beating the United States to gold in the volleyball.
The upsets spread to the pool where Chinese divers Qiu Bo and Lin Yue could not better the efforts of American David Boudia in the 10m event. Qiu won silver and Britain's Tom Daley, cheered on by English soccer player David Beckham, took bronze.
But there was no surprise in the women's basketball where the U.S. claimed a fifth straight gold by thrashing France 86-50 to extend their Olympics winning streak to 41 games.
In the ring, Ukraine's Oleksandr Usyk claimed the men's heavyweight crown while classy light-welterweight Roniel Iglesias Sotolongo won Cuba's first boxing gold in eight years and Britain's Luke Campbell took the bantamweight title.
The hosts have claimed 28 gold medals, comfortably beating their Beijing tally of 19. It puts them third in the overall medals table, which the United States top on 44 to China's 38.
With one day of Olympian effort left, Sunday's highlights include the toughest running event - the marathon - and the showcase men's basketball final, which sees pre-tournament favorites the U.S. taking on a dangerous Spain side.
Organisers have less than 24 hours to prepare the stadium for the closing ceremony, which artistic director Kim Gavin said would celebrate British pop music from the last 50 years.
The Spice Girls, One Direction, George Michael and The Who are expected to perform as London prepares to bid goodbye to what the Guardian newspaper dubbed the "feelgood Games".
Games chief Sebastian Coe declined to compare London with other Olympics, but said simply: "I'm pretty pleased with the way we've delivered."
"Party, party, party," he told a news briefing when asked to describe the closing concert ending a drama-filled few weeks.
Forecasters point to a warm and dry day in London to bring to a close a festival of sport that has helped to lift the gloom in recession-hit Britain.
As well as a "hit list" of more than 30 popular songs, the closing ceremony will feature thousands of athletes and performing volunteers as well as a section devoted to the next summer Olympic hosts, Rio de Janeiro.
"I think it's a gift that we've got Rio next because their eight minutes is so wonderful and really full of that samba beat," Gavin said of the 2016 hosts.
(Reporting by the Reuters Olympic team; Editing by Ken Ferris)