Kate Allen was unaware her astonishing run in the final leg of the women's Olympic triathlon on Wednesday had put her in a position to win Austria's first gold medal of the Athens Games.

The 34-year-old, who was born in Australia and took on the nationality of her husband Marcel Diechter two years ago, moved up from 28th after the cycling leg to overtake race leader Loretta Harrop 150 metres from the line.

"It was the run of my life," she said. "I had a good group in the cycling. Swimming was perfect. In the cycling, the other women worked harder than I had expected, and the running was a surprise. I had such a great feeling today."

Allen's pace in the sweltering heat allowed her to work her way through the field until she got into the medal positions behind Australian Harrop, who had led from the start.

"I was in third place but I didn't know," she said. "My husband told me: 'You're running for a silver medal. Do you know that?'

"Then I saw Loretta 200 metres before the finish line and she wasn't going that fast and that was my gold medal."

"I would have been pleased with a top-five finish today," added Allen, who took up triathlon in 1996 after meeting Diechter while travelling around Europe.

"I gave it everything today," she said. "Everything came together. It was a perfect day."

Harrop, who had been working in tandem with American Sheila Taormina, was disappointed to miss out on gold.

"It was a big strange, the swimming and bike didn't go as planned, I thought Sheila would be a bit stronger, I was doing most of work," said the 29-year-old silver medallist.

"I knew I'd beaten most of the girls on the world circuit and so was pretty confident," she added. "But there are athletes that don't race throughout the year."

American Susan Williams came third despite crashing her bike in the middle leg of the race.

"I got a bit too excited trying to catch the two girls in front and when I braked the wheel just slipped away," she said.

"I got a couple of scrapes but Barb (Lindquist) waited for me so it worked out pretty well.

"I was the dark horse even to make the U.S. team so I am thrilled."