LONDON - China stayed clear on top of the Olympic medals table on Sunday as two more world records tumbled in the swimming pool.

Following an impressive opening day, the Chinese captured two gold from shooting and diving on Day 2, leading the medals race with six gold, four silver and two bronze. The United States followed with 11 medals, including three gold.

Italy, South Korea, France, DPR Korea and Kazakhstan all have two gold to be joint third.

Guo Wenjun, who was back to shooting four months after giving birth to a girl last year, retained her women's 10-meter air pistol title, earning China its second gold at the Royal Artillery Barracks.

Guo won the qualifying round but was down to third with two rounds left in the final. But the 2008 champion got back to top in the last shot when then leader Celine Goberville of France faltered.

"I was very nervous throughout the final," said Guo. "I told myself to calm down and tried to stay focused."

The all-conquering Chinese divers started their bid for a clean sweep of eight gold medals as Wu Minxia and He Zi won the women's 3-meter synchronized springboard title.

The world champions led all the way to amass 346.2 points, ahead of US pair Abigail Johnson and Kelci Bryant (321.9) and Canada's Emilie Heymans and Jennifer Abel (316.80).

"We managed to stay composed during the final, and encouraged each other in every dive," said Wu.

If the 26-year-old Wu wins the 3-meter springboard event, she will equal retired Guo Jingjing as the most successful diver with four Olympic gold.

Kazakhstan landed their second gold in these games thanks to a former Chinese national.

Zulfiya Chinshanlo, who moved to Kazakhstan from China's Hunnan province in 2008, won the women's 53kg title after breaking her own clean-and-jerk world record with a lift of 131kg.

The 19-year-old Chinshanlo was in tears on the podium.

"Those setbacks and pains I have endured over the years came across my mind," Chinshanlo told Xinhua.

At the Aquatic Center, American Dana Vollmer won the women's 100m butterfly gold in 55.98 seconds, eclipsing the previous world mark of 56.06 set by Sweden's Sarah Sjostrom in 2009.

China's Lu Ying settled for the silver in 56.87 seconds and Australia's Alicia Coutts grabbed the bronze in 56.94.

South Africa's Cameron van der Burgh matched Vollmer's feat by breaking the men's 100m breaststroke world record in the final. The 24-year-old's winning time of 58.46 seconds was 0.12 better than the mark set by Brenton Rickard of Australia in 2009.

In basketball, the NBA star-studded US team eased past France 98-71 in their opener, while China staged a rare brilliant show against European champions Spain before losing 97-81.

Elsewhere, cyclist Lizzie Armitstead won Team GB's first London 2012 medal, taking silver in the women's road race.

Armitstead, 23, was beaten at the end of the 140-kilometer race by Dutchwoman Marianne Vos in a sprint finish on The Mall.

But the hosts suffered a blow when women's marathon world record holder Paula Radcliffe withdrew from the Games because of injury.

Off the competition, Luiza Galiulina, a female gymnast from Uzbekistan, has been suspended after being caught for using the diuretic furosemide, the second positive case of these Games.

It came a day after the International Olympic Committee expelled Albanian weightlifter Hysen Pulaku after he tested positive for the banned steroid stanozolol on July 23.