SWIMMING/World Championships:Michael Phelps scooped up his fifth gold medal at the World Championships yesterday but is still to face his toughest test.

The 21-year-old American stayed on course to win an unprecedented eight titles in Melbourne when he made it five from five with victory in the 4x200 metres freestyle relay.

Phelps combined with Ryan Lochte, Klete Keller and Peter Vanderkaay to win the final in a world record time of seven minutes 03.24 seconds to add to gold medals in 4x100 freestyle, 200 individual medley, 200 butterfly and 200 freestyle.

Phelps is an overwhelming favourite to win the 400 metres individual medley tomorrow and pick up another gold in the concluding medley relay but today's 100 metres butterfly final is looming as his biggest obstacle.

He qualified fourth fastest for the final after conserving his energy for the relay but has his work cut out beating his Texan team-mate Ian Crocker.

Crocker is the world champion and world record holder for the event and underlined his domination by heading the qualifying list for the final in 51.41 seconds, more than half a second ahead of Phelps (51.92).

Lochte, meanwhile, stepped out of the shadows of his lauded team-mates by winning two individual gold medals.

Lochte, with two silvers under his belt, turned the tables on Aaron Peirsol by reversing the result of the 100 metres backstroke final and winning gold in the 200 metres in a world record of one minute 54.32 seconds, slicing 0.12 seconds off Peirsol's mark.

He then teamed up with Phelps, Keller and Vanderkaay as the US quartet wiped 1.42 off the 4x200 metres freestyle record of 7:04.66 set by Australia at the 2001 World Championships.