Five-time world champion Ronnie O'Sullivan saw his BetVictor Welsh Open title defence end at the hands of Matthew Stevens at the third-round stage.
O'Sullivan was edged out 4-3 by the Welshman at Cardiff's Motorpoint Arena after surrendering a 2-0 lead.
Stevens got himself back into the match by edging a scrappy third frame before levelling with a break of 80 in the fourth.
O'Sullivan took the next to move within sight of victory but then missed a crucial yellow to allow Stevens back to 3-3 and the home favourite prevailed in the decider.
O'Sullivan had been critical of the venue earlier in the week, likening the ambience to a car boot sale, but did not make any excuses for his loss.
He said: "The venue is all right. You get used to it. It's the same for both players - good crowd, good atmosphere. I'm just disappointed to have lost."
O'Sullivan also paid tribute to his opponent's performance after losing to Stevens for the first time in 12 years.
He said: "Matthew played a good match, he deserved his win. He has had a lean few years. He is a great player, under-achieved really. So, credit for Matthew - playing in Wales, Cardiff. I can only say well done to him. He is having a good tournament.
"Unfortunate for me but that's snooker - you win some, you lose some."
World number one Mark Selby, winner of the German Masters earlier this month, reached the last 16 by seeing off veteran Peter Ebdon 4-3 in a tight match lasting four minutes short of three hours.
Neil Robertson, the 2010 world champion, also came through a difficult match against Jamie Cope 4-3 while Ali Carter survived a Matthew Selt fightback to go through by the same scoreline.
Another former world champion, Mark Williams, won his all-Welsh clash with Jamie Jones 4-2 and will play world number six Judd Trump, who battled through a tight encounter with Michael Wasley 4-2.
Marco Fu overcame Ashley Carty 4-2 to set up a meeting with Stevens while John Higgins enjoyed a comfortable 4-0 win over China's Liang Wenbo.