Latin American sides clash in men's final but Mexico are without star forward Dos Santos due to injury.
Olympics: Neymar aims to find Brazil's missing football gold
Brazil have not been this close to the gold medal in football since Romario was a young promising star in the late 1980s.
Many great players have tried and failed after him, including the likes of Rivaldo, Roberto Carlos, Ronaldo and Ronaldinho.
Now it will be up to Neymar, the future of Brazilian football, to try to end decades of frustration and give the nation its first gold, the only trophy missing in football for the five-time world champions.
Brazil are favourites going into today's final at Wembley Stadium against Mexico, a team which has had unusual success against their Latin American rivals in recent years and will also be looking for a first Olympic gold.
Mano Menezes, the Brazilian coach, said: "We all know that we need to win the gold
"Brazil has to win every tournament it plays, it needs to win every match it plays, even if it's a friendly. And this time even more because it's something the nation has never won before."
Brazil are playing in an Olympic final for the first time since the 1988 Seoul Games, when the team led by Romario and Bebeto lost 2-1 to the then Soviet Union. Brazil also lost the final four years earlier in Los Angeles, and never again made it this close to victory.
Bebeto, Ronaldo, Rivaldo and Roberto Carlos got the bronze at the 1996 Atlanta Games, and Ronaldinho also finished third with Brazil four years ago in Beijing, when the team lost in the semi-final to Argentina.
Coaches who tried and failed to deliver gold include Mario Zagallo in 1996, Vanderlei Luxemburgo in 2000 and Dunga in 2008.
The man carrying the team's expectations this time is 20-year-old Neymar, Brazil's most talked-about player in recent years, touted by many to potentially become the best player in the world.
"We came here for the gold and we are one match away from getting it," said Neymar, who has been playing up to expectations so far with three goals and several assists in the team's five victories so far. "We just have to do our job in the final."
But Brazil will be facing opponents who have caused them many problems in recent years.
Mexico have won six of the last 12 matches against the Brazilians since 1999, including that year's Confederations Cup final.
They lost only four of those games and drew two.
The Mexicans won the last time the teams played, a warm-up for the Olympics just a few months ago in the United States. Mexico won 2-0 in a match in which both teams played with many of the players who made it to the London Games.
But Mexico's task to win their first gold has been hampered following a hamstring injury to star forward Giovani Dos Santos, who has been ruled out of the final. The son of a former Brazilian player, Dos Santos will be replaced by Marco Fabian.
"It's sad, but even if he can't be there, we are going to play the match for him and the country," the defender Miguel Ponce said.
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