Whichever nation the supporters inside the Olympic Stadium were cheering for, there was a collective standing ovation for a history-making South African athlete yesterday. Oscar Pistorius, instantly recognisable as the so-called "blade runner" or the "fastest man on no legs" running on artificial limbs, became the first double amputee to compete at the Olympic Games.

And by posting a second-place finish in a 400m heat, he is guaranteed a place in tomorrow's final. "I've run so many times in the UK and it feels like a second home to me," he said.

The 26-year-old's legs were amputated below the knee just before his first birthday and he has won four titles at the Paralympics. He has competed at the World Athletics Championships but this was his first time at the Olympics.

"I have always said it is one thing being here and another thing performing here, and that is what I have been concentrating on," he said. "I want to represent my country well. I worked very hard for what I am able to achieve. I have been blessed with a talent that has enabled me to get to the Paralympics and the Olympics, but really it is all about the people around me. I have been with my coaching team for nine years; my friends and family are so patient with me. Everyone around me has put so much into my career."

The defending champion in the 400m, LaShawn Merritt, did not finish his heat after suffering a hamstring injury. Pistorius is also due to compete in the 4x400m relay track event.

For those still without Olympic tickets, there was an early start for one of the free events at Hyde Park. The women's triathlon led to the closest margin of gold medal victory of the Games so far – and one of the narrowest in Olympics history – with a photo finish at the finishing tape. Switzerland's Nicola Spirig and Sweden's Lisa Norden were given the same finishing time after the 1,500m swim around the open water of the Serpentine, a 43km cycle and 10km run around Constitution Hill and the Mall. Spirig was given first place on the width of her running vest.

British hope Helen Jenkins fell away during the final running leg of the course and came in a respectable, if personally disappointing, fifth. She revealed that she sustained an injury during training in the final weeks before the Olympics that had hampered her chances. "I didn't know my form when it came to the run and it was a bit of an unknown," she said. "I gave it everything but I couldn't hang on. It's been a rough 10 weeks. Everything that we didn't want to happen did happen – a bad swim, a crash, a puncture and injury."

There was disappointment in the trampolining hall as well. British No 1 Kat Driscoll, 26, from County Durham, finished ninth in a competition won by Canada's Rossannagh Maclennan. She said: "No one wants to finish ninth, do they? I did the best routines I could do but they just weren't good enough today. I am so pleased I did what I did and I am proud of my routines. I just enjoyed the experience. I did not feel a weight of expectation from the crowd or pressure. I just felt they were giving me a big hug and taking care of me."

There were encouraging signs for Great Britain, however, in the show-jumping as Nick Skelton and Ben Maher both started strongly in the qualifying stage in Greenwich Park. Only the top 60 riders move into the second of five rounds of competition, which runs into next week. It is Skelton's sixth attempt to win Olympic gold and has been posted as the favourite among bookmakers on his horse Big Star.