UPDATE 1-Olympic-Swimming-Phelps and U.S complete relay sweep

By Simon Evans

BEIJING, Aug 17 (Reuters) - Michael Phelps won a unprecedented eighth gold medal in the Beijing Games on Sunday as the U.S broke the world record in a thrilling 4x100 metres medley relay to complete a clean sweep of the men's relay events.

The U.S team of Aaron Peirsol, Brendan Hansen, Phelps and Jason Lezak posted three minutes, 29.34 seconds, shaving 1.34 of the previous world record set by the U.S. in Athens.

The Australians took silver, in 3:30.04 with Eamon Sullivan pushing Lezak hard on the final freestyle leg.

Japan took bronze in 3:31.18

With the victory, Phelps eclipsed compatriot Mark Spitz's 1972 record of seven golds in a single Games.

(Editing by Greg Stutchbury)