Michael Phelps has won his eighth Olympic gold medal at Beijing to succeed Mark Spitz as the best swimmer of all time.

The 23-year-old capped a breathtaking nine days of superfast swimming at the Water Cube by helping the US smash the world record in the 4x100 metres medley relay.

The victory helped Phelps better Spitz's record haul of seven golds from the 1972 Munich Olympics and lift his overall tally to 14, five more than any other athlete, after his six from Athens four years ago.

He said: "I wanted to put my mind to it and wanted to do something that no one ever did in sport. Nothing is impossible - with so many people saying it couldn't be done, all it takes is an imagination."

After surviving two nailbiting finishes to get to seven golds, and earn a £536,000 bonus from his sponsors, the medley relay was considered a relative formality for Phelps.

The US have won the event at every Olympics, except for 1980 in Moscow when they boycotted, and were never in any real danger of losing this time.

Aaron Peirsol, breaststroker Brendan Hansen and freestyler Jason Lezak, joined Phelps to win the gold in a combined time of 3:29.34, slashing 1.34 seconds off the old world record.

Australia finished a close second with Eamon Sullivan making up ground on the final freestyle leg while Japan finished third.

Australia also set a world record to win the women's medley relay and finish with six golds, second only to the US which won 12 in total. The two relay world records lifted the final tally set in the Water Cube to 25.

Backstroker Emily Seebohm, breaststroker Leisel Jones, butterflyer Jessicah Schipper and freestyler Libby Trickett wiped more than three seconds off Australia's previous world record to win the gold in 3:52.69.

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