Beijing 2008- Phelps breaks own record in first heat

The 23-year-old clocked four minutes 07.82 seconds to break his own record in the first heat and reach the finals on Sunday.

"I wasn't expecting heats to be that fast. But getting that first race under your belt feels really good," Phelps said.

Phelps is on course to amass a record eight gold medals for the US this summer, following his gold medals in Athens 2004.