The Northern Ireland Open has already delivered the kind of first-round drama that can reshape a tournament. Ronnie O'Sullivan led qualifier Ka Wai Cheung 3-1, then lost the final three frames as the world number 110 claimed a 4-3 win. Later, world number three Judd Trump also went out 4-3, beaten by Martin O'Donnell, ranked 56th, who earned his first victory over the former world champion.
Monday's first-round exits, verified against BBC Sport and MyiCue match records
Cheung won the last three frames after trailing 1-3.
The Hong Kong qualifier recorded his first main-draw knockout win at a ranking event.
O'Donnell took the deciding frame for his first win over Trump.
BBC Sport reported that eight of the nine top-16 players who had played at the venue had already lost.
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