South African Oscar Pistorius paid tribute to his late mother on Saturday saying that without her instilling solid values in him he would never have achieved his dream of competing at the Olympics.

The 25-year-old was speaking after he made history by becoming the first double amputee to compete in an athletics event at the Olympics.

Pistorius, who trumped the moment by also qualifying for the 400 metres semi-finals, was watched in the stands by his 89-year-old grandmother, waving a South African flag, whom he saluted warmly.

But he admitted his thoughts had turned to mother Sheila, who left an indelible mark on him before she died 10 years ago.

"I thought about my mother a lot today," said Pistorius, who fought a long battle to be allowed to compete at an Olympics running on his carbon fibre blades.

"She was a bit of a hardcore person. She didn't take no for an answer.

"She always said the loser isn't the person that gets involved and comes last but it's the person that doesn't get involved in the first place."

South Africans glowed with pride on Saturday as they watched him become the first double amputee to compete in the Olympics.

"We are proud of him, especially being the first time a double amputee competes with able-bodied athletes," said Sifiso Magagula, 29, sipping a cup of coffee at a restaurant in Braamfontein in downtown Johannesburg.

"And for him to qualify second in a sport dominated by Americans and Jamaicans... we are so proud of him," said Magagula, flanked by his wife.

While the race did not pull big crowds at a huge television screen mounted between a hotel and a coffee shop on a sunny winter morning, those present coould not hide their excitement.

"It's a monumental time for a disabled man to compete in able-bodied athletics," said Jason Handle.

One fan even tried to draw parallels with Nelson Mandela's historic release from prison in 1990. The anti-apartheid icon went on to become South Africa's first black president four years later.

"This was an awesome experience watching Oscar, it's a historic moment, and I say it's almost like watching Mandela walk out of jail after 27 years, for a Paralympic athlete to be part of the actual Olympics ... awesome!" screamed 41-year-old Mary, one of the dozen enthusiasts who watched him run.

Pistorius, who had both legs amputated below the knee before he was aged one, because of a congenital condition, runs on carbon fibre blades.

He is also due to run in the 4x400m relay at the Games.

Ivan Lukhele, a quantity surveyor, said initially he had harboured doubts that Pistorius would make it past the first round.

"At first I didn't give him any chance. Since now he has qualified I am so excited. It's amazing, you know there are many lessons that we can learn from him.

"It shows that anything is possible as long as you put your mind and energy to it," said Lukhele.

Pistorius competed in the Athens 2004 and Beijing 2008 Paralympics.

He was only given the green light to make his debut in the Olympics following studies that found his prosthetics afforded him no advantage over his able-bodied rivals.

He clocked 45.44sec in his first-round run and is hoping to smash his personal best of 45.07sec and dip below the 45-second barrier, the true mark of world-class 400m running.