Stephen Maguire, the defending champion, described his performance as terrible, after suffering an unexpected 5-3 defeat at the hands of fellow Scot Alan McManus in the last 16 of the Malta Cup today.
"I think that's as bad as it gets. I can't remember playing that badly before," said Maguire, who was hoping to become only the 11th player to retain a world ranking event title.
"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. I just need to forget about it as quickly as possible."
Maguire, who came to prominence by beating Jimmy White in last year's final at the same Portomaso Hilton venue, was a shadow of the player who so convincingly won the UK Championship in November to move to 3rd on the provisional world list.
"I can't put my finger on what went wrong but I just couldn't do anything. Alan won but I don't think he'll be happy with his performance."
Maguire, a 23 year-old Glaswegian who practises at the city's Q Club along with McManus, gave no inkling of what was to follow as he secured the opening frame in confident fashion with an 89 break.
It was downhill from there, though. Maguire was guilty of several key errors as McManus, down to 21st in the provisional rankings and fighting against relegation from the elite top 16, established a 3-1 lead at the mid-session interval.
That became 4-2 when Maguire was guilty of an awful safety shot on the yellow in the sixth but he regrouped to salvage the seventh with a late run of 46.
In recent seasons McManus has not been the most reliable frontrunner but on this occasion, after another grossly misjudged Maguire safety, the former Benson and Hedges Masters champion stepped in with a match clinching run of 83 in frame eight.
McManus, who has not added to his two world ranking event triumphs since the 1996 Thailand Open, 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."
In his first quarter-final appearance since the Welsh Open 13 months ago McManus will play Welshman Matthew Stevens, who did enough to break down the stubborn resistance of Mike Dunn, a qualifier from Redcar.
At 3-3 Stevens, without a win this season until beating Shaun Murphy 5-4 in the first round on Monday, looked vulnerable.
But he scrambled through a marathon seventh frame that dragged on for 37 minutes and controlled a low scoring eighth to advance.
