American Dana Vollmer won the 100 butterfly in a world record and was followed by Cameron van der Burgh of South Africa, who set a world mark to win the 100-metre breaststroke.
"I'm on top of the world right now." Vollmer said. "I still know I can go faster."
But the biggest surprise at the Aquatics Centre came from France's 4x100-meter freestyle relay team, which upset the favoured United States and Australia.
The Americans led almost all the way until Yannick Agnel pulled ahead of Ryan Lochte in the final lap. France clocked 3 minutes, 9.93 seconds, and the Americans settled for silver in 3:10.38. Russia took bronze in 3:11.41, with pre-race favourite Australia fading to finish fourth.
Spain's under-23 football team, hoping to add Olympic gold to the country's senior world and European titles, was eliminated after an upset 1-0 loss to Honduras in Newcastle.
Host country Britain picked up its first two medals of the London Games, with Beijing Olympics champion Rebecca Adlington taking silver in the 400-meter freestyle after cyclist Lizzie Armitstead finished second in the rain-slickened road race.
Earlier, Kevin Durant scored 22 points and Kobe Bryant added 10 as the latest incarnation of the U.S. basketball's latest edition of the Dream Team beat France 98-71 in its tournament opener with first lady Michelle Obama cheering in the stands.
LeBron James, who had eight assists for the Americans, said the effort was far from perfect.
"We had too many turnovers, too many fouls and we had a couple of defensive rebounds we could have come up with," James said. "But overall, we played a pretty good game for as close to 40 minutes as possible."
After a week of sunshine, heavy rain on the second day of competition affected the start of tennis on the lawn courts at Wimbledon and gave horses problems in the dressage portion of the three-day event.
That wasn't the only issue. Organizers responded to intense public criticism by offering tickets to local school children and soldiers who stepped in to guard the games after it emerged that blocks of prime seats were being left empty at Olympic venues that are reportedly sold out.
Organizing chief Sebastian Coe said the troops and students would fill the gaps.
In the 140-kilometre road race held in mostly pelting rain, Armitstead took silver behind Marianne Vos of the Netherlands.
Vos, a former world champion, made a daring move past Russia's Olga Zabelinskaya to emerge from a three-rider breakaway on the last straight near Buckingham Palace.
"It is the most special thing I have ever experienced," Armitstead said of cheering local fans who braved the terrible weather along the route. "It was crazy, so inspiring."
The joy of Britain's first medal was tempered by news from the country's athletics federation that its top marathoner, Paula Radcliffe, has pulled out of the Aug. 5 race due to a foot injury.
While the weather was bad, there were other problems: a female gymnast from Uzbekistan was provisionally suspended after failing a doping test, the second case of the games. The IOC says Luiza Galiulina tested positive for the diuretic furosemide on Wednesday. It came a day after the IOC expelled Albanian weightlifter Hysen Pulaku from the games after he tested positive for the banned steroid stanozolol on July 23.
St. Kitts & Nevis sprinter Tameka Williams was sent home by her team for a potential drug violation. Williams had been using a substance which was "clearly outside the medical code," St. Kitts Olympic committee vice-president Dennis Knight told The Associated Press.
Knight said Williams had not tested positive, but the team acted after consulting with the World Anti-Doping Agency "to find out about the product," which was not disclosed.
Hundreds of fans wanting to see New Zealand, Brazil, Belarus and Egypt were stranded in London or forced to sit on the train floor Sunday as service operators supplied only two morning London-to-Manchester services in time for the noon kickoff of the New Zealand-Egypt match in Manchester, 200 miles (320 kilometres) northwest of London.
At Wimbledon in southwest London, the new retractable roof came in handy as pouring rain halted all but 12 matches. On uncovered Court 1, 2008 bronze medallist Novak Djokovic endured two long delays en route to a win over Fabio Fognini of Italy, 6-7 (7), 6-2, 6-2.
"I haven't played an official match since Wimbledon, so it took me a set and a half to really get into the rhythm," said Djokovic, seeded No. 2. "Obviously the rain delay affected the game, and I wasn't sharp enough after the rain delay."
Maria Sharapova won her Olympic debut, beating Shahar Peer of Israel 6-2, 6-0 on the protected Centre Court, and Andy Murray returned to the court where he lost the Wimbledon final to Roger Federer earlier this month. Murray beat a Swiss this time. overcoming Stanislas Wawrinka 6-3, 6-3.
Three-time gold medallist Venus Williams, No. 1-seeded Victoria Azarenka and Andy Roddick all had their matches postponed.
In the first of 14 gold medals on offer Sunday, shooter Guo Wenjun defended her women's 10-meter air pistol title, giving China its second gold at the range.
Kimberly Rhode won the gold medal in women's skeet, making her the first American to win an individual-sport medal in five consecutive Olympics.
An Kae Um won North Korea's first gold medal of the games in the women's judo 52-kilogram category. The 20-year-old An defeated Acosta Bermoy of Cuba in the final in a match that went into overtime.
Elsewhere, the 3-meter synchronized springboard was won by Chinese divers He Zi and Wu Minxia.
At the Olympic equestrian complex, Zara Phillips, granddaughter of Queen Elizabeth II, had a few royal fans in the stands as she made her equestrian debut.
Phillips' grandfather, the Duke of Edinburgh, as well as her mother, Princess Anne, were in the VIP seats at Greenwich Park as Phillips rode her horse, High Kingdom, through the paces of a standard dressage test.