Former champion Shaun Murphy suffered a shock 6-3 defeat to China's world number 124 Chen Feilong in the first round of the UK Championship in York.
Murphy, who won the tournament in 2008 and was also runner-up in 2012 and 2017, surrendered a 3-1 lead in the match as his poor start to the season continued.
Murphy said: "I didn't see that coming because I have been practising so hard, and my preparations for this event have been fantastic.
"I have had a terrible season so far but that has left me a lot of time to practice and I feel my game is in such good shape - but I'm still waiting for that to come through."
Another former winner, Jimmy White, saw his hopes of a run in the tournament brought to an end in a 6-3 defeat to Thailand's Thepchaiya Un-Nooh.
White, 56, now ranked 77 in the world, put up an encouraging performance against Un-Nooh, scoring three breaks over 50 including a 97 to temporarily threaten a comeback before his opponent finished the job.
World number 12 Ryan Day was another surprise loser as he went down 6-2 to world number 121 Joe O'Connor, while former world champion Stuart Bingham swept through with a 6-0 thrashing of James Wattana.