World number one Ronnie O’Sullivan crashed out of the World Championship in the first round after suffering a stunning defeat to amateur James Cahill.

In arguably the biggest shock in the tournament’s history, Cahill held his nerve to beat five-time champion O’Sullivan 10-8 at the Crucible.

O’Sullivan was a prohibitive favourite before the match after a season which saw him win five titles and compile his 1,000th career century on his way to victory in the Tour Championship.

But after recovering from 8-5 down to get back on level terms with the aid of breaks of 104 and 89, O’Sullivan missed a great chance to snatch the 17th frame and Cahill took advantage to move 9-8 in front.

O’Sullivan looked on course to set up a final-frame decider only to inadvertently pot a red when breaking the pack open from the blue, leaving Cahill to produce a nerveless break of 53.

During the match it was very clear that O'Sullivan wasn't at his physical best, appearing to look tired and fatigued throughout, something which he confirmed afterwards.

He said he was struggling to stay awake during the last session, and his behaviour has come under heavy criticism from snooker legend Ken Doherty.

Doherty, who won the title in 1997, said the world number one did not look well during the 10-8 loss.

"He played very casually, it was almost with a lot of disrespect in a way," BBC pundit Doherty said about Monday's first session which Cahill led 5-4.

"He didn't want to be there, didn't look like he fancied the job.

"The most important thing for Ronnie and for snooker is that he's healthy.

"He doesn't look well, didn't play to his best. The game is tough when you're not feeling good."

Despite the negativity surrounding O'Sullivan, nothing should be taken away from Cahill.

The 23-year-old from Blackpool will face Scotland’s Stephen Maguire in the second round.