ADELAIDE - Ian Thorpe's rushed comeback bid for a third Olympic Games ended in ignominy on Sunday as he crashed out of the morning heats of the 100 metres freestyle at the Australian trials in Adelaide.

Australia's Ian Thorpe reacts after the men's 200m freestyle semi-finals at the 2012 Australian Swimming Championships to qualify for the 2012 London Olympics, in Adelaide March 16, 2012. [Photo/Agencies]

The five-times Olympic champion, who also failed to secure a spot in the 200 freestyle earlier in the trials, won his heat but finished 21st in the timings behind pace-setter and world champion James Magnussen in his last-chance saloon for London.

The 29-year-old's time of 50.35 seconds was his best since returning to competition in November, but was more than two seconds shy of Magnussen's and left him well outside the top 16 that will compete at the semi-finals in the evening session.

On Friday, Thorpe described his failure to qualify in the 200, his best chance for London, as a "fairytale turned nightmare", but was somewhat less dramatic as he contemplated the final nail in the coffin for his Olympic dream.

"This is... it's tough. It's hard coming to this competition and really, you know, failing in what I set out to do," he told reporters at the South Australia Aquatic and Leisure Centre.

"I'm disappointed that I really haven't been able to race in a way that's reflective of the work that I've done and how I've trained.

"But I don't regret giving this a go. Compared to how I've raced before, how I've competed and the success that I've had, this does look like doom."

"But I'm glad I was willing to put myself out there to give this a shot. I'm pleased with that part, and disappointed that it hasn't been the result that I wanted."

The headline act at the trials, Thorpe took a long time to exit the pool after winning his heat, the ninth of 12, and walked into the bowels of the arena to await his fate.

In the end there was little suspense, as almost all of the remaining swimmers smashed the 50 second mark to leave the swimmer a spectator at London, little more than a year after announcing his return to the pool.

"Thorpie's been someone I've always admired as a swimmer, so it is upsetting for him and the rest of us to do feel his pain," Olympic gold medal favourite Magnussen told reporters.

"It would have been great to have him there in London, it's disappointing that he's not going to be there, but all I can do now is focus on my race."

On Friday, Thorpe failed to reach the final of the 200 freestyle, a result that left a packed crowd stunned and left the swimmer hugely disappointed.

The 11-times world champion's 200 bid was easily his best chance to qualify for London and although he put on a brave face after that failure, he conceded he was battling against the odds to break into the top six of the 100, which would have given him a chance of selection for the relay team.