Ronnie O'Sullivan showed tremendous fighting qualities to defeat Mark Williams 13-11 and book a semi-final clash with Graeme Dott in Sheffield.
O'Sullivan is a two-time world champion
O'Sullivan resumed 10-6 ahead having racked up breaks of 56, 72, 68, 109, 95 and 70 in the afternoon session.
Williams surged back, winning five of the first six frames in the evening, before O'Sullivan made a run of 90.
Williams had chances in the 24th frame but could not take advantage as O'Sullivan closed out an epic match.
It was O'Sullivan's performance in the middle session that put him on the verge of victory, but any thoughts that he would then coast to victory were quickly dispelled.
Williams levelled the match at 11-11 without doing anything spectacular and could have gone 12-11 ahead.
But, leading by 37 points in frame 23, the Welshman missed a red to the middle and O'Sullivan stepped in with a superb 90 clearance.
And despite failing to sink the black off its spot when on 43 in the next, the 30-year-old from Essex got back in to finally kill off Williams' hopes.
"Mark is the toughest opponent I've ever faced," said two-time champion O'Sullivan, who beat Dott in the 2004 final.
"Other top players have major weaknesses but he has bottle and character in abundance and showed that again tonight.
"He never once let up and I just had to hang in. I was kept off the table so much because he kept potting long balls.
"It's a shame there had to be a loser but it's a great confidence-builder for me."
Williams was delighted with his display and also paid a glowing tribute to O'Sullivan.
"I put him under loads of pressure but he made an excellent break to go 12-11 up. Not many players could have done that," said the 31-year-old from Cardiff.
"I had him on the rack and couldn't have asked any more of myself. If I'd had a little run of the balls it could have gone my way.
"It was an excellent match all the way through and I think I've lost to the winner of the event. He looks so confident."
M Williams (Wal) 11-13 R O'Sullivan (Eng)
0-90 (90) 94-0 (94) 64-56 68-0 (67) 2-60 73-4 (68) 11-85 (55) 19-89 (79) 42-70 (56) 1-72 (72) 12-68 (68) 77-0 8-109 (109) 116-4 (74) 0-95 (95) 1-85 (70) 65-55 (O'Sullivan 55) 63-4 59-66 67-11 85-8 (78) 58-17 37-90 (90) 18-62