Though the South African swimmer, still just 20, was hotly tipped to take home medals from London, his stunning victory in 1:52.96 at the Aquatics Centre was still one of the major shocks of the Games.
The scale of his achievement, and what it meant to him, was obvious on the podium, where he shed tears of emotion.
Afterwards he said: ‘This is a dream of mine, I have always said Michael Phelps was my hero. I wanted to be in the final for my main event, I achieved that goal and my coach said you have done all you have to do.
‘But I just remember sitting in the call room thinking that Michael Phelps has never lost this race for 10 years in international meets.
‘I remember turning in the last 50 and just looking at him underwater and realising this is my hero, it’s crazy.
‘I can’t describe how I felt. In the last 25 metres, I can’t explain what came over me.
‘I’ll have to try and defend my title in four years time, but to beat Michael Phelps is something I have wanted my whole life.’
Le Clos, who began swimming competitively aged 10, is one of South Africa’s most exciting Olympic prospects. His potential became clear when he won five medals at the Youth Olympic Games and the Commonwealth Games in 2010 while still a schoolboy – followed by gold in the 200m Butterfly at the World Short Course Championships in Dubai.
In November 2011 he took the overall Fina World Cup title in Japan, joining his countrymen Ryk Neethling and Cameron van der Burgh in capturing the prestigious title, despite only being included as a late replacement.
And at the South African National Swimming Championships ahead of London 2012 his multiple qualifying times even eclipsed established star Van Der Burgh.
Le Clos competed in six events in London – a record for his country – and added silver in the 100m Butterfly to his 200m gold. Now he is being groomed for glory at Rio in 2016, and without the almost invincible Michael Phelps in the pool, his chances of bagging more gold medals are significantly raised.
But no matter how the powerful freestyler fares in four years’ time, it’s likely that his besting of the most decorated Olympian of all time will remain a career highlight.
He said: ‘Eight years ago when I was a 12-year-old boy who looked up to Michael Phelps as a hero, or more like a god. I didn’t think I’d be up here talking about beating him. My coach Graham Hill and I call it destiny.’