Ronnie O'Sullivan suffered the seventh whitewash of his career on a day of shocks at the Malta Open.
O'Sullivan beat Dott 18-8 to win the 2004 world title
The world number one was beaten 5-0 by Graeme Dott, who lost to O'Sullivan in last year's World Championship final.
"I was outplayed and outscored. It's difficult to motivate yourself when you don't feel comfortable with your game," said O'Sullivan.
World number seven Ken Doherty also went out of the tournament in the last 16, beaten 5-2 by outsider Tom Ford.
And Stephen Maguire's defence of his title came to an unexpected end at the hands of fellow Scot Alan McManus.
O'Sullivan potted only one ball in the first two frames and rashly conceded the third while leading 25-0 after missing a simple pink to a middle pocket.
Dott stepped in to take the fourth with a run of 114 and although he broke down on 63 in the fifth, he later potted yellow and green to get over the winning line.
"Even before the start of the match I got the impression that Ronnie wasn't there but I still had to go out and do a job," said Dott.
"I'm glad I won by playing well because I'll get the credit for beating him.
"I feel as if I'm playing well enough to win the tournament. Put it this way - I wouldn't want to play me."
Dott will now play Steve Davis, who defeated Stuart Pettman 5-3.
Ford, world-ranked 74th, reached the first quarter-final of his career after contructing breaks of 90, 71, 59 and 51 against Doherty.
"It's easily the best win of my career," said Ford, who now faces Stephen Hendry.
Doherty admitted he had been outplayed.
"I'd never seen him before but he played very well," he said. "He potted some great balls and whatever he went for seemed to go in."
Maguire, the world number three, described his 5-3 defeat to McManus as the worst performance of his career.
"I think that's as bad as it gets. I can't remember playing that badly before," said Maguire.
"Towards the end I was actually embarrassed and wanted to get out of there as quickly as possible. It was a terrible day for me."
McManus agreed that Maguire had been the architect of his own downfall.
"It was a good result but we both made lots of mistakes. Stephen was well below par to what he's been lately. He was giving me chance after chance," he said.
In his first quarter-final appearance since the Welsh Open 13 months ago McManus will play Welshman Matthew Stevens.
Stevens defeated qualifier Mike Dunn 5-3.