Mark Williams fought back from 4-1 down to see off Matthew Stevens 6-4 and advance to the quarter-finals of the Betfair Masters.
Williams was out of sorts, losing four of the first five frames to his fellow Welshman, and he was dangerously close to losing the sixth frame as well.
However, Stevens missed a simple brown to go 5-1 in front and from then on committed numerous basic errors as Williams took five frames in a row to secure an unlikely victory.
Former world championship finalist Stevens looked in complete command of a low-quality match when he led by three frames with five played and made a break of 59 in the sixth frame.
Williams made 37 to get back into the frame before missing a straight yellow, but Stevens then missed an equally easy frame-ball brown to let his fellow Welshman off the hook.
The left-hander improved from then on and runs of 59 and 68 helped him into a 5-4 lead, while he sealed victory with breaks of 48 and 44 after Stevens had missed a black off the spot.
World number one Mark Selby produced a superb fight-back in the evening match at the expense of Stuart Bingham.
Selby trailed 5-1 but reeled off five frames in a row to win 6-5 and set up a last-eight clash with former world champion Williams.
After Selby took the opening frame with a break of 63, Bingham assumed command of the match as runs of 55, 78 and 86 took him 4-1 in front.
The Basildon right-hander then came out on top in a protracted safety battle on the colours in the next to move within one frame of victory.
However, Selby belatedly began to find some form and breaks of 57, 86 and 68 got him back on level terms as Bingham started to feel the pressure.
Bingham was first in after an excellent opening red in the decider, but badly missed a blue into the top corner to let Selby in.
And although he needed three chances, the Leicester cueman eventually wrapped up an unlikely victory and celebrated with a clenched-fist salute towards friends and family in the crowd.