BEIJING (AFP) - South African Olympic swimmer Natalie du Toit won her fifth gold of the Beijing Paralympics Sunday as China established what looks likely to be a decisive lead at the top of the medals table. But the Games were hit by more controversy when a British athlete was stripped of second place over a classifying issue in the women's discus. Du Toit took the women's 50 metres freestyle in a Paralympic record time of 29.20 seconds, finishing 0.13sec ahead of Russia's Irina Grazhdanova and matching her haul in the 2004 Athens Games. "I was very nervous, I knew it was going to be tight. Coming down the straight I didn't look anywhere in the pool," the 24-year-old said. "My race was to go out there and concentrate on the start and the finish and I think I got my finish right for once. My start was a little frustrating." Du Toit's victory in Sunday's sprint follows victories in the 100m butterfly, 100m freestyle, 200m individual medley and 400m freestyle events in her class. "I think right now it's more the relief than thinking about five gold medals. It's not really about the medals, it's about going out there and doing personal best times. I'm happy with my performance," she said. Elsewhere in the penultimate night of action in the pool, Erin Popovich of the United States just missed out on matching du Toit, finishing just 0.08secs behind compatriot Cortney Jordan in her class of the 50m freestyle. And Australia's Matthew Cowdrey won his fourth gold in the men's 50m freestyle. Du Toit, who finished 16th in the Olympic 10 kilometre marathon swim, is one of only two athletes to compete at both Beijing Games along with Polish teenager Natalia Partyka, who won table tennis gold in her class. In the "Bird's Nest" National Stadium, wheelchair racer Canada's Chantal Petitclerc continued her success, winning the 800m to go with earlier golds in the 100m, 200m and 400m. China had 63 golds and 159 medals in total on Sunday evening - matching its tally of 63 golds at the Athens Games and 22 golds clear of second-placed Britain. Controversies have taken some of the gloss off what has otherwise been a celebration of disabled sports, led by the performances of du Toit and "Blade Runner" Oscar Pistorius in front of huge crowds. Britain's Rebecca Chin, entered in a cerebral palsy class, finished the women's discus final in the silver medal position but her name was subsequently struck from the scoresheet. An International Paralympic Committee (IPC) spokeswoman said: "The athlete showed significantly different skill sets and subsequently the chief classifier lodged a protest under exceptional circumstances. The athlete is found not eligible, not matching the sport class profile."British chef de mission Phil Lane called for more opportunities to classify athletes outside of major competitions. Games chiefs, however, managed to avoid the embarrassment of having to rehold the medals ceremony, as has been done twice during these Paralympics. On Saturday the Iranian wheelchair basketball team forfeited their quarter-final clash with the United States, saying they were unhappy with the draw and schedule for the later rounds. And Irish sports chiefs Thursday announced that athlete Derek Malone had been banned from the Paralympics because authorities had deemed him not disabled enough. So far four athletes, including three powerlifters, have been kicked out of the Games for doping offences. A total of 715 doping tests had been carried out at the Games, both in and out of competition, by the end of Friday. At the Athens Games, a total of 680 doping tests were conducted, resulting in 10 violations. More than 4,000 competitors from nearly 150 countries and regions are battling for 472 gold medals in 20 sports at the Paralympics.