By Ian Gordon, PA Sport, Sydney

Wonderboy Ian Thorpe filled his Olympic swag-bag with double gold as Australia won their opening day confrontation with the United States in Sydney on Saturday.

The 17-year-old smashed his own world record in the 400m freestyle and then anchored his relay team to a thrilling victory over their bitter American rivals.

"This is the proudest moment of my life," he said after winning his first Olympic title.

"I had to swim hard but I knew I was in great form and the record proves it.

"It's an incredible feeling. It's an honor to get this gold for the country.

"This is the proudest moment of my life," Thorpe said.

"I had to swim hard, but I knew I was in great form and the record proves it."

Thorpe, who at 15 became the youngest world champion in the sport's history, said his first Olympic gold medal was unique.

"Nothing compares to winning the gold medal.""

Thorpe beamed with the delight after winning the first of expected four golds that will set him on the path to becoming the greatest swimmer in history.

But the Aussie smiles were even wider as he snatched victory in the 4x100m freestyle relay in another world record time as the defending champions were sunk by the human 'thorpedo'.

The Sydney superkid with with size 17 feet was just over 0.6 secs adrift of Gary Hall junior as they turned for the final 50metres in the relay, but Thorpe began catching the American with every stroke to win by a fingertip.

As it was Hall who said before the Games that their rivals would be smashed 'like guitars' in the pool, the Australian foursome of Michael Klim, Chris Fydler, Ashley Callus and Thorpe revelled in the victory.

It was the first time the Americans had been beaten in the event at the Olympics.

Thorpe had stopped the clock at 3:13.67 secs to carve 1.5 seconds off the Americans' five-year world record.

The beaten quartet were also inside the record with 3:13.86 but it was scant consolation and their disappointment showed in the medal ceremony before Hall stepped off the podium to shake hands with his rivals.

The teenager had been roared on by cries of 'Thorpey, Thorpey' from the 17,500 sell-out crowd in the International Aquatic Centre as he powered his way to victory in the 400m freestyle.

Thorpe, who had smashed the Olympic record in the heats, carved 0.74 secs off the world record he had set in the same pool last May to win in three minutes 40.59 secs.

Wearing his full-length bodysuit Thorpe won by almost three seconds from Italy's Massimiliano Rosolino, whose time of 3:43.40 made him the second fastest man ever.

Thorpe has now set seven world records in his home pool at 200m and 400m freestlye in the last 13 months.

American Klete Keller finished almost seven seconds down to take grab the bronze by just 0.01 sec from Italy's Emiliano Brembilla.

Britain's Paul Palmer, silver medallist four years ago, discovered that the world of freestlye swimming has moved on since Atlanta as he crashed out in the heats.

Palmer finished over three seconds outside his British record when finishing third in three minutes 51.06 secs to miss out on a final spot by two places.

"I was bitterly disappointed after all the preparation that's gone into this," said the University of Bath swimmer who competes in the 200m in the early hours of Sunday when Thorpe will again be favourite.

"I felt relaxed and fast in the warm-up. Perhaps in hindsight I was a little too fast in the first 200m. When I needed the speed it was not there."

Elsewhere, the 4x100m freestyle relay quartet of Karen Pickering, Alison Sheppard, Rosalind Brett and Sue Rolph twice smashed the British record as they finished fifth in the final.

The foursome clocked 3:40.54 to come within 0.24 secs of the third placed Swedes while American Jenny Thompson led her team home to gold in a world record time of 3:36.61.

Thompson has earlier set an Olympic record in the 100m butterfly, but saw it beaten twice in quick succession in the heats and semi-final by Dutch sensation Inge de Bruijn.

The 27-year-old, whose massive improvement since coming out of retirement has inevitably led to speculation about the methods used, lowered the mark to 57.14 secs.