Just 18 months after seriously injuring her knee and putting her chances for London at risk, Mustafina won the title on uneven bars Monday. It gave the 2010 world champion a full set of medals, following her silver in the team competition and bronze in the all-around.
Brazil's first gold medal came in judo on July 28, Australia's first in swimming on the same day. Nine days later, they have their second.
Arthur Zanetti preceded Mustafina on the gold podium at the gymnastics venue, beating the "Lord of the Rings'" — defending champion Chen Yibing of China — in the still rings. It was only Chen's second loss in six years and gave Brazil its first-ever gymnastics gold at an Olympics.
"I was the last gymnast to compete and I stayed calm and took my moment," said Zanetti.
Far from London on the English Channel, Australian sailor Tom Slingsby gave the team from Down Under gold No. 2.
Slingsby won the men's sailing Laser class at Weymouth, England.
Australia, having one of its worst games, hoped to finish among the top five in gold and overall medals. But until Monday, it had only a women's relay win in the swimming pool on the first full day of competition.
Pavlos Kontides, who finished second to Slingsby, made some history of his own, winning the first-ever Olympic medal for Cyprus. Xu Lijia won gold in the women's race in the same class.
Jason Kenny gave Britain its fifth gold medal at the London Velodrome by outclassing world champion Gregory Bauge in the final of the men's sprint, track cycling's marquee event.
Kenny, who had never beaten Bauge before, justified the British team's decision to enter him in the event instead of defending champion Chris Hoy by beating Bauge 2-0 in the best-of-three final.
Britain beat the Netherlands in a jumpoff for the gold medal in team show jumping, the host side's first gold medal in the discipline in 60 years. Saudi Arabia took bronze.
Three members of Britain's four-man team — Nick Skelton, Ben Maher and Peter Charles — rode clear rounds in the jumpoff to give the host team the victory.
Skelton said he was more nervous watching his teammates than riding himself.
"I wish I could have gone four times," he said. "They've done great. I've got a wonderful horse, wonderful owners, it's a dream come true."
Defending Olympic 50-kilometre race walk champion Alex Schwazer has been caught doping and will miss the race here. And American judo competitor Nicholas Delpopolo was expelled from the Olympics after testing positive for cannabis.
In athletics Monday, Algerian middle-distance runner Taoufik Makhloufi was excluded from the rest of the Olympics for not trying in an 800-meter heat. Makhloufi stopped on the first lap Monday, appearing to be saving energy for the 1,500 final on Tuesday where he was a likely medal contender.
The International Association of Athletics Federations said its race referee found Makhloufi guilty of "failure to compete honestly with bona fide effort" and now he won't be able to compete in either race pending any appeals.
The 24-year-old Makhloufi, who is African champion over 800, had already won his heat and semifinal in the 1,500.
He is disqualified a week after four women's badminton doubles teams were disqualified for playing to lose.
In better news from the track, world champion Sally Pearson of Australia set the early standard in the women's 100-meter hurdles, clocking the fastest first-round time in the event in Olympic history.
Pearson posted a time of 12.57 seconds to qualify for the semifinals, with the final scheduled for Tuesday night at the Olympic Stadium.
"It's really nice to have support when you're on the other side of the world," Pearson said. "I was nervous about the first race. There's no more work to do, this is it. Tomorrow is another day at the office ... I want to get it done and dusted."
On Monday night, pole vaulter Yelena Isinbayeva will try to defend her Olympic title as effectively as 100-meter champion Usain Bolt did on Sunday night.
The Russian star will be going for an unprecedented third straight Olympic gold in London on Monday. No woman in track and field has managed to win three individual Olympic titles in three successive games.
In the women's football tournament, Japan beat France 2-1. The World Cup champions will play the winner of Monday night's later semifinal between the United States and Canada for the gold medal.