Antrim's Mark Allen suffered a surprise 4-3 defeat by 16-year-old Yan Bingtao in the third round of the English Open, while Joe Swail and Fergal O'Brien also bowed out.
The Pistol is currently ranked at number eight in the world, while Bingtao is at 98, and in his first season on the World Snooker Tour.
Allen, 30, said afterwards: "People [are] continually playing well against me but [I'm] just not getting the rub of the green at the minute.
"I know it'll turn if I keep working hard."
Swail lost 4-2 to Tom Ford, while O'Brien was beaten by Liang Wenbo on the same scoreline.
The event, in Manchester, is part of the new Home Nations series with the winner receiving a trophy named after snooker great Steve Davis, the six-time Crucible king who retired in April.
Ronnie O'Sullivan is also out after a 4-3 loss to Chris Wakelin.