The eight-day Olympic swimming programme starts with a bang tomorrow with US star Michael Phelps and his arch rival Ryan Lochte on a collision course in the men's 400m individual medley.
Phelps' haul of eight gold medals from the Beijing Olympics four years ago included the 400m medley title, but the 27-year-old swim legend was beaten by Lochte, the reigning world champion, at the US trials three weeks ago.
Competition at the Aquatics Centre kicks off tomorrow morning with the men's medley heats, and the final is the first race of the evening session.
Phelps is aiming to become the first male swimmer to win a gold medal in the same individual event in three successive Olympic Games and will not surrender his crown without a fight.
"It's going to be a very challenging and exciting race, I have changed a few small things to see if it will help (since the US trials)," said Phelps, who has amassed 14 Olympic gold medals.
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"I am feeling good, I am feeling confident. It is going to be a fun one to start. You can guarantee it will be loud on opening night," said Phelps.
Most interest centres on whether Phelps can repeat his golden Beijing form against the in-form Lochte, who took the 400m medley gold at last year's world championships in Shanghai, an event Phelps sat out.
"For anyone who wants to promote swimming, there is not a better way in the world than for (Michael Phelps) to swim the first race in the first (swim) event at this Olympic games," said his coach Bob Bowman.
"It will be a coaches' and spectators' dream to see how that shakes out."