Selby, who had won three of the past four titles, was unable to find his form as Perry clinched a surprise 10-4 victory at the Crucible Theatre in the English city.

The Englishman had given himself too much to do as he trailed 4-0 and then 7-2 going into the evening session.

Perry, the oldest player competing at the tournament at the age of 43, held his nerve to secure a famous triumph.

"When the draw came out, it is one of your two worst nightmares," Perry told BBC Sport.

"I knew I had to perform at the best of my ability today and I did for the most part. 

"A few nice bits of luck were on my side today which I capitalised on and am very pleased with my performance.

"It must be horrible for him, I have lost here plenty of times and never been reigning champion."

Snooker star Ronnie O'Sullivan, a five-time World Championship winner, is also facing an early exit as he trails 6-3 to Scottish qualifier Stephen Maguire.

The 42-year-old Englishman has had one of the best seasons of his career, winning five ranking titles so far.

His meeting with Scotland’s Maguire is a repeat of their first-round clashes at the Crucible in 2004 and 2005, both of which were won by O’Sullivan.

But he needs to produce a comeback tomorrow if he is continue his pursuit of a sixth crown.

Elsewhere, Scotland's Graeme Dott leads England's Ali Carter 6-3 going into tomorrow.