Defending champion Shaun Murphy was dumped out of the Masters in the first round by Mark Allen at Alexandra Palace.
Murphy, who beat Neil Robertson in the final last year, fought back from 5-2 to 5-4 but both men made errors in a scrappy 10th frame that eventually went the way of Antrim cue star Allen as he secured a 6-4 victory.
After the first two frames were shared, Allen moved ahead with a break of 137 in the third and then made it 4-2 when Murphy forfeited the frame following three misses.
Another century of 104 put Allen one frame away and, although Murphy managed a break of 100 in the ninth frame, he could not complete the comeback.
Allen will face either Barry Hawkins or Joe Perry in the quarter-finals.
Murphy stood by his decision to try the same shot for a third time in the costly sixth frame.
Because he was not snookered, his third miss meant he automatically lost the frame.
He said on worldsnooker.com: “It’s the rule. You don’t see it very often. Normally you would look for an alternative on the third go. I couldn’t see a Plan B.
“All other options left him a guaranteed chance so I had to man up, take a deep breath and play the right shot. Unfortunately I got it completely wrong.
“Did I lose the match because of it? No, I don’t think so. There were plenty of other frames.
“I thought it was a really good match played in very good spirit. That match could have been the final of any tournament. Unfortunately for me it was the first round and I’m on my way home.”
Allen was thrilled to beat his good friend in one of snooker’s biggest tournaments.
He said: “Shaun is the defending champion here, under a lot of pressure, and it was a big match for me playing him on the big stage.
“I’m very happy with the way I played, I scored heavily, took my chances well and got over the line in the end.”