Roddick was beaten 6-3, 6-4 by Jonas Bjorkman, the veteran Swede, with the American producing a thoroughly disappointing mistake-prone performance.

He returned serve poorly, too often allowed Bjorkman to take the initiative and pile forward to the net, and even played two indifferent games with a service regarded by many as the best in the world.

Roddick did have the excuse of the breeze, which blew sand on to the court, and made conditions tricky.

There was no question that a phlegmatic Bjorkman took his chance steadily and well, but the American looked as though his mind might already be on the Australia Open in Melbourne the week after next.

The first signs of an upset came in the sixth game when Roddick allowed a Bjorkman lob sail over his head for a winner and then allowed his opponent to attack him to reach break point.

Bjorkman converted that at the first attempt as Roddick launched a forehand drive long and flung down his racket fiercely in annoyance.

It soon became clear that this anger was unlikely to spark a recovery as Bjorkman then broke again in the opening game of the second set as Roddick again played a surprisingly uncertain game from the baseline.

Once in the fifth game of that set Roddick stopped after attempting a passing shot because he apparently thought Bjorkman was certain to make a winning volley, only to restart when he realised he had a chance to reach the ball.

But the split second delay proved fatal and the lost point hinted at the uncharacteristic uncertainty and oddly passive reactions from the American.

"I'm always going to have off days," he reckoned.

"I am playing against the best in the world on a daily basis, so it's going to happen. He played well and I was far from my best.

"There was a change in the conditions. There was a kind of a haze and I couldn't figure it out. I wasn't seeing it well. It was just one of those days.

"I was glad to get straight into some doubles here. I also have some matches in Kooyong, so I should have enough before the Australian Open."

Bjorkman said afterwards: "It's always difficult to play the number one in the world but I faced him twice last year and I think I learnt how to play him. I managed to put a lot of pressure on him.

"I think the key was I served very well and got many free points of which you need against the number one in the world. I think I played very well today and this gives me a lot of confidence."

Roddick was the fifth of the eight seeds to depart the tournament, with Rainer Schuttler, the number two from Germany, Mark Philippoussis, the number four from Australia, Nicolas Massu, the number five from Chile and Younes El Aynaoui, the number six from Morocco, all having been beaten on the first two days.

Only three remain.

They are Sebastien Grosjean, the number four from France who is the new favourite and now plays Ivan Ljubicic of Croatia; Tim Henman, the number seven from Britain who faces Sargis Sargsian, the US-based Armenian, and Agustin Calleri, the number eight from Argentina, who plays Bjorkman.

The other quarterfinal pits Korea's Hyung-Taik Lee, who pulled off a great result beating last year's champion Stefan Koubek in straight sets, against wild card entrant Nicolas Escude of France.