Ireland's David Morris beat Mark Selby 6-4 to knock the world champion out of the UK Championship in York.
Selby, who became a father for the first time earlier this month, is set to lose his world number one ranking spot following his second-round exit.
The win against the 2012 champion was the biggest scalp yet for Morris, who is ranked 62 in the world.
Nigel Bond came from 5-0 down to beat Barry Hawkins 6-5 while Ding Junhui saw off Jimmy White 6-2.
Morris clinched victory with a match-winning break of 79 in the 10th frame and had earlier fired a match-best 126 against Selby, who was runner-up to Neil Robertson last year.
"I didn't think I played well at the start and deserved to be 3-1 behind," said Selby. "I played better after the interval and so did Dave and on the day he deserved to win.
"I know the potential he has and should be better than he is doing. He showed what a great player he is out there.
"If there are any positives about the loss, then it is that I can go home and spend more time with my daughter."
Morris admitted he was nervous all the way through the match.
"Even at 3-1 up, I was shaking on shots because I am not so used to being on the big stage," he said. "To beat someone of Mark's class is a big feather in my cap.
"I had a few good wins last year but you can't compare it to this because it is such a big win for me in front of a packed audience on TV."
Elsewhere Ricky Walden, Judd Trump, Mark Williams, Matthew Stevens and John Higgins were among those to progress.