Updated

Great Britain's Iain Percy and Andrew Simpson turned in a pair of top-two finishes Tuesday in the Star class sailing event at the London Olympics, but hold a slim lead in the competition.

Percy and Simpson, the defending gold medalists, won Tuesday's first race ahead of Brazil's Robert Scheidt and Bruno Prada. The Brazilians then beat the Brits in the second race.

After six of 10 preliminary races, Percy and Simpson lead the competition with 21 points. Scheidt and Prada had 23, and both seem to be in great position to head into the medal race.

Most of the sailing events in the Olympics are, like the Star (keelboat), fleet races. Each boat participates in 10 races, where points are awarded in ascending order -- 1 for 1st, 2 for 2nd, and so on. After the 10 races, each boat's worst performance is discarded, the remaining points are tallied, and the 10 best boats advance to the medal race.

In the Finn (men's heavyweight one-person dinghy), Denmark's Jonas Hogh- Christensen continued to make himself a favorite for the medal race. He finished first and second, and has a double-digit lead over Great Britain's Ben Ainslie -- the two-time defending gold medalist.

Ireland's Annalise Murphy again won both of the races in Laser Radial (women's one-person dinghy), to take a staggering lead after four races. She has four points, compared to 16 for second-placed Evi Van Acker of Belgium. Murphy finished 25th at the world championships this year.

The USA's Paige Railey sits in ninth after four races in Laser Radial.

Australian Tom Slingsby, the reigning world champion, is still atop the standings in the Laser (men's one-person dinghy) competition after four races.

Australians Nathan Outteridge and Iain Jensen moved up to first after four races in the men's 49er (skiff), thanks to a pair of top-four finishes Tuesday.

Australia is leading in the women's Elliott 6m -- a new match racing sailing event comprised of 12 crews. It won twice Tuesday to improve to 6-0 in the round robin stage, after which the best eight boats move on to the knockout stage.

Meanwhile, the United States boat skippered by Anna Tunnicliffe improved its chances of advancing. The Americans defeated Finland and France by a combined seven seconds, moving to 4-2.

The two RS:X (windsurfer) classes got underway Tuesday. The Netherlands' Dorian van Rijsselberge won both men's races to jump into first place, while American Robert Willis is in seventh. In the women's competition, Spain's Marina Alabau Neira leads after finishing second and first.