Oscar Pistorius told his doubters to "look at the clock" after running a world record on his return to London and Paralympic competition tonight.

And he then stirred up controversy by questioning whether one of his rival's running blades might give him an advantage.

The South African, who last month became the first amputee sprinter to compete in an Olympics, clocked 21.30 seconds to win his heat of the T44 200m with effortless ease.

His crossover into non-disabled competition has made the Blade Runner a Paralympic icon and he received a huge ovation from the capacity crowd at the Olympic Stadium.

His time was a personal best and Pistorius admitted it took him by surprise.

"I couldn't have hoped for a better return here," he said. "I didn't expect to run a time like this tonight.

"I've run my fastest time and I eased off about 20 metres from the end because I knew I was comfortable and I wanted to conserve energy for (the final) tomorrow.

"Everybody was saying, 'how can you peak for both (the Olympics and Paralympics)?'

"I've proved everybody wrong tonight, running a world record. If there were people that doubted by goals then go and look at the clock, it says 21.30."

Pistorius then questioned whether the International Paralympic Committee would have to look again at their blade rules after American Blake Leeper came storming past his South African team-mate Arnu Fourie in the previous heat.

Pistorius, who had to win a legal battle with the IAAF over his blades to be able to compete in the Olympics, suggested athletes were making themselves taller by using as long blades as possible.

"The rules allow the guys to make themselves a lot longer, longer than they would have been," he said.

"It is difficult, you saw Blake Leeper overtaking. He was five metres behind Arnu Fourie, he finished three metres ahead of him.

"I don't know what's happening there. Don't take away from his performance, I think he's a great athlete, but it's very clear that the guys have got very long strides."

The South African also hailed the atmosphere in the stadium, claiming it was as good as it had been for the Olympics.

The only man to compete in both said: "The crowd is exactly the same, as passionate, as exciting.

"It fees like you might as well be running in the Olympics. It's mind-blowing."