Jack Lisowski opened the defence of his Northern Ireland Open title with a 4-1 win over Huang Jiahao, but Mark Selby slipped to a first-round defeat against Louis Heathcote.
Selby took the first two frames with breaks of 54 and 70, but Heathcote responded with two half-centuries of his own before closing out victory to move into the last 32.
Earlier at Waterfront Hall Sam Craigie made two century breaks as he edged out Xiao Guodong in a last-frame decider, while Anthony McGill beat fellow Scot Stephen Maguire 4-1.
Wang Xinbo saw off compatriot Si Jiahui and Ireland’s Aaron Hill slipped to a 4-2 defeat against Thepchaiya Un-Nooh. Matthew Selt came from behind to beat Hossein Vafaei 4-3 and Poland’s Mateusz Baranowski battled past Gary Wilson in the final frame.