BEIJING, August 10, 2008 (AFP) - Michael Phelps electrified the Water Cube on Sunday, earning his first gold medal of the Beijing Games with a stunning world record in the 400m individual medley.

The 23-year-old American, aiming to improve on swimmer Mark Spitz's Olympic standard of seven gold medals at one Games, was cheered on by US President George W. Bush, who turned out to see Phelps outgun Hungarian Laszlo Cseh and fellow American Ryan Lochte in the first swimming final on the Beijing programme.

Phelps didn't disappoint, clocking 4min 03.84sec and slicing 1.41sec off the previous world mark of 4:05.25 that he set at the US trials in June.

He admitted that Lochte and Cseh were too close for his comfort at the halfway stage - after the butterfly and backstroke legs.

Lochte, swimming two lanes over, briefly edged ahead in the breaststroke, but Phelps asserted himself and closed out his rivals with a majestic finishing freestyle.

'I came off the last wall and it was the same feeling as in Athens,' Phelps said. 'I saw myself out there and I smiled. I knew the first one (gold medal) was there.'

Cseh, lying a close third most of the way, overtook Lochte for the silver, clocking a European record of 4:06.16. Lochte took the bronze in 4:08.09.

Resting at the pool wall, Phelps smiled and raised an arm in triumph. From his perch in the VIP section, Bush signalled congratulations.

'It was cool,' Phelps said of the presidential salute. 'That was a cool feeling to have the President here and to say congratulations.'

'That was a pretty emotional race,' said Phelps, the subject of intense scrutiny for months as he readied his assault on the record gold tally Spitz set in Munich in 1972.

To break it, he'll have to swim at least 17 times over the nine days of competition as he goes for gold in five individual events and three relays.

'I think I am as prepared as I can be at the moment,' he said.

With his medley triumph, Phelps successfully defended one of the six titles he won four years ago in Athens.

On Sunday night he turned in a conservative performance in the heats of the 200m freestyle, notching the fourth-fastest time heading into the semi-finals.

'Tonight was just about getting to tomorrow,' said Phelps, who was an underdog when he took bronze in the event in Athens but is now the world record-holder.

Looking at tough opponents coming up, he singled out Park Tae-Hwan, who triumphed in the men's 400m freestyle to give South Korea its first Olympic swimming gold.

Park, who received telephoned congratulations from South Korean President Lee Myung-Bak after winning in the second-fastest time in history of 3:41.86, will also tackle the 200m free.

In the 400, the 18-year-old sensation held off a fast-closing Zhang Lin of China, who exhilarated the 17,000 crowd by taking silver in 3:42.44. American Larsen Jensen was third in 3:42.78.

Australian Stephanie Rice opened her debut Olympic campaign in sensational style, with a women's 400m individual medley world record of 4:29.45.

It was a gutsy performance from the swimming glamor girl, who was almost four seconds under the world record at the halfway point before she staved off a last lap surge from Zimbabwe's Kirsty Coventry.

Coventry, swimming out in lane one, was also under the previous world record, taking silver in 4:29.89, while Katie Hoff, who had set the world mark of 4:31.12 at the US trials in June, settled for bronze in 4:31.71.

'I turned around and I thought I saw 4:31 on the clock,' Rice said. 'The first thing that went through my mind was 'that hurt a lot for a 4:31,' but when it all clocked over and I realised I had swum a 4:29, I thought 'that's amazing!''

While Phelps was taking it easy in the evening heats, his teammates in the 4x100m freestyle relay heats were providing plenty of fireworks, with a world record time of 3:12.23.

Nathan Adrian, Cullen Jones, Ben Wildman-Tobriner and Matt Grevers lowered the mark set by a US quartet at the 2006 Pan Pacific championships in Victoria, Canada - and set the stage for a spectacular final on Monday morning.

In the final, top US trials performers in the 100m free - Jason Lezak, Garrett Weber-Gale and Phelps - were expected to take over to complete the task of gaining the gold that eluded them in Athens.

France and Australia, also without their top sprinters in the heats, were also under the previous world record.

There was no world record but there was gold in the women's 4x100m free final for the Dutch team of Inge Dekker, Ranomi Kromowidjojo, Femke Heemskerk and Marleen Veldhuis.

They had already set the world record in winning the European title in March, and gilded that achievement with Olympic gold with a victory in 3:33.76.

The US quartet of Natalie Coughlin, Lacey Nymeyer, Kara Lynn Joyce and 41-year-old Dara Torres took silver in 3:34.33.

Australia, gold medallists in Athens, earned the bronze as Cate Campbell, Alice Mills, Melanie Schlanger and Libby Trickett finished in 3:35.05.