- Ryan Lochte wins gold in the 400m individual medley
- 14 time Olympic gold medal winner Phelps finishes a disappointing fourth
- Brazilian Thiago Pereira claims silver, Kosuke Hagino takes bronze for Japan
Ryan Lochte won the United States' first gold medal at the London Olympics with an outstanding performance in Saturday's 400m individual medley.
Swimming superstar Michael Phelps, who has 14 Olympic gold medals from his three previous Olympics, could only manage fourth place in a disappointing performance.
"I think I am in shock right now. Going into these Games I knew I was capable of getting the win. I'm happy that I was able to do that," said Lochte.
The rivalry between Lochte and Phelps has dominated the build up to this year's swimming competition, but Phelps couldn't live up to the hype as he struggled to find the form that helped him win eight golds in eight days at the 2008 Beijing Olympics.
With First Lady Michelle Obama in attendance, Lochte, the current Fina male swimmer of the year, dominated the race from the start.
The six-time Olympic medal winner, including three golds, opened up an early lead and never looked liked being caught in the race that combines four different strokes.
Phelps hasn't missed out on a medal since finishing fifth in the 200m butterfly at the 2000 Sydney Olympics, but he ends day one empty handed after finishing behind surprise medal winners Thiago Pereira and Kosuke Hagino.
"It was just a crappy race. They swam a better race than me, they swam a smarter race than me and that is why they are on the podium," said Phelps, who is scheduled to compete in seven events at the Games.
"It's just really frustrating to start off on a bad note like this, it's pretty upsetting."
"The biggest thing now is to try and get past this and move forward. I have a bunch of races and hopefully we can finish this a lot better than we started.
Brazilian Pereira won his first Olympic medal, having previously competed at the 2004 Athens and 2008 Beijing Olympics.
Japanese Kosuke Hagino, a 17 year old, won the 200m individual medley at last year's Fina junior World Championships and wasn't expected to even reach the final in London.