Top seed Mark Allen crashed out of the Duelbits Players Championship in the first round after suffering a 6-3 defeat to Joe O'Connor.
World number 37 O’Connor belied his status as the lowest-ranked player in the 16-man field with a number of cool clearances to book his place in the quarter-finals in Wolverhampton.
Three breaks in the 60s, including a superb 64 to steal frame two, helped O’Connor into a 4-1 lead before Allen, who has won three rankings titles this season, reduced his deficit with a break of 91.
A total clearance of 132 took O’Connor 5-2 ahead and although Allen won frame eight to keep the match alive, he ran out of position in the next and O’Connor stepped in with a 45 clearance to seal victory.
The 27-year-old from Leicester will face either Luca Brecel or Jack Lisowski in the last eight.
"I’m over the moon at the minute," O’Connor told ITV4. "He beat me in the (World) Grand Prix so it was nice to get a little bit of revenge.
"I don’t think Mark played his best today, I had a few extra chances that I probably shouldn’t have but I’m happy with the way I played and I punished him."
Allen was left to rue a number of missed chances and said: "It was a match of what could have been really.
"I was in in a lot of frames and didn’t make the most of my chances and played some really poor safety as well. It’s disappointing for me but credit to him."
Second seed Ryan Day made sure there would not be another upset on the opening day as he compiled breaks of 88, 102 and 53 in beating Chris Wakelin 6-2.
Day will play either Mark Selby or Shaun Murphy in the next round.
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