World number one Mark Selby was sent crashing out of the UK Championship by 22-year-old amateur James Cahill in one of the tournament's greatest shocks.

Cahill, who dropped off the tour in 2017 and is currently without a ranking, stormed into a 4-0 lead before wrapping up a 6-3 first-round victory with a stunning long pink.

The Blackpool player had beaten Ding Junhui on his way to the fourth round of the same tournament four years ago but subsequently considered quitting the sport after a streak of poor results.

Cahill said: "I felt a bit of pressure out there and I just thought I had to go for my shots because if you don't go for your shots against Mark Selby, you're never going to win.

"I've had some difficult times but I'm convinced I'm good enough to compete with the best and I think I've showed that. Now I've got to shift my focus and concentrate on the next round."

Selby described his own performance as "rubbish" and was at a loss to explain a display which leaves his top ranking in jeopardy, with Mark Williams – who beat Adam Duffy 6-2 – set to take over if he goes on to win the title.

"I had some chances but everything just kept falling awkwardly," said Selby. "I'm devastated and it feels weird – I just couldn't get myself up for the match and I felt really flat out there."

Ronnie O'Sullivan avoided the same fate but revealed he was suffering from a virus after brushing aside factory worker Luke Simmonds to book his place in the second round.

Despite losing the first frame to his unranked 38-year-old opponent, O'Sullivan appeared to show few ill effects as he rattled in back-to-back centuries for a 6-1 win and set up a Sunday clash with fellow veteran Ken Doherty.

But afterwards O'Sullivan said he felt "absolutely awful" and at one stage became concerned he might have to curtail his quest to become the first player to win the title seven times.

"At one point today I wondered if I was going to get through it," said O'Sullivan. "I couldn't focus on the balls – I just had to grind it out really and wait and see what happened.

"It felt like one of the hardest matches I've ever had to play. Every time I was on a shot I felt like I was going to feather the white because I couldn't focus. Every shot felt like a black ball in a world final."