London - South Africa's Oscar Pistorius made history on Saturday and realised his lifelong dream when he became the first double amputee to compete in an athletics event at the Olympics.Video: Oscar Pistorius - Men's 400m Round 1 Heats The 25-year-old qualified for the semi-finals of the 400m by running a season's best of 45.44sec in finishing second, a performance made extra special as his 89-year-old grandmother was in the crowd.Pistorius, who had both legs amputated below the knee before he was aged one, because of a congenital condition, runs on carbon fibre blades."It's just an experience to be here. It's a dream come true," said Pistorius, whose time was the 16th fastest overall."I’ve worked for six years to try and make the 400 metres standard."It's just an unbelievable experience. I found myself smiling on the starting blocks which is very rare and as I came out of the tunnel I saw my friends and family here."Most important of all for him was the presence of his ageing grandmother, who has been a seminal influence on him since his mother died 10 years ago."My grandmother, she's 89, she was here with the South African flag. It was just an amazing experience."My mother was such a big part of my life and my grandmother was out here today. My family's just been a huge... support."Pistorius, who had set himself the goal of reaching the semi-finals, said that it was hard to place this among his many other remarkable experiences in competition."I've had some experiences which I hold very dear to my heart," he said."My first Paralympic Games in Athens (2004) is still probably one of the highlights of my career."I was a 17-year-old kid with curly hair and braces. I didn't know what to expect and that was just mind-blowing for me and I didn't even know the guys I was running against."He is also due to run in the 4x400m relay at the Games.Pistorius, who is 13kg lighter than when he competed in the Beijing Paralympics, admitted he had found it difficult to keep his mind on the race itself."It's very difficult to separate the occasion from the race."The kind of pressure that you put on yourself coming into a competition like this is massive. It's sometimes difficult."It started sinking in a couple of days ago - and I felt butterflies."Pistorius, who will stay on in Britain after the Games to compete in the Paralympics, said the occasion had almost overwhelmed him."I was so nervous this morning," he said."I didn't know whether to cry. I had a mixture of emotions."Pistorius suggested that the wait to compete at an Olympics had given him time to polish up his performances so he would not be embarrassed on the biggest stage of them all."As you progress your goals become harder and harder and your career and your knowledge becomes greater and you start fine-tuning everything from training to diet to rest and recovery."Pistorius, known as the 'Blade Runner', was given the green light to make his debut in the Olympics following studies that found his prosthetics give him no advantage over his able-bodied rivals.His personal best is 45.07sec in the 400m and Pistorius came to London wanting to break the 45-second barrier.He is clear to compete on condition he uses the same prosthetic legs that have been used in Paralympic sport since 1996.But Pistorius said exhaustive tests had proved that running on blades gave him no advantage."If I had to listen to the five percent of negativity, I wouldn't be here," he said. "If I have such an advantage, why isn't everybody else running the same times?"