Scotland's Stephen Maguire lost 4-0 to Thailand's Thepchaiya Un-Nooh in the first round of the English Open.
World number 14 Maguire reached the semi-finals in 2018 but only scored 62 points in four frames against a player 27 places below him in the rankings.
Un-Nooh hit breaks of 86, 65, 117 and 75 to reach the second round of the tournament at the K2 in Crawley.
Elsewhere, there were victories for top-10 players Mark Williams, Neil Robertson, Mark Allen and Kyren Wilson.
Three-time world champion Williams had been level at 2-2 with Jamie Clarke but won the next two frames, including a break of 142 in the sixth, to clinch the match 4-2.
World number seven Wilson made breaks of 95 and 72 in his 4-2 victory over China's Liang Wenbo, Northern Ireland's Allen lost the opening frame but went on to beat Thailand's James Wattana 4-2, while Australia's Robertson secured a routine 4-0 success over Wales' Kishan Hirani.
The 1997 world champion Ken Doherty was beaten 4-0 by Hong Kong's Marco Fu, while six-time world finalist Jimmy White, 57, lost 4-2 to 17-year-old Chinese player Bai Langning.
Reigning champion Stuart Bingham is among those in action on Wednesday as he faces China's Si Jiahui in the second round.
Five-time world champion Ronnie O'Sullivan, who has repeatedly criticised the facilities and lack of atmosphere at the West Sussex venue, plays 19-year-old Yuan Sijun of China.
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