Mark Williams ended an eight-year wait for victory over Ronnie O’Sullivan by storming back from a three-frame deficit to win their Masters quarter-final 6-5.

Williams’ hopes of beating the seven-time Masters champion and world number one seemed distant as O’Sullivan surged into a 3-0 lead at Alexandra Palace on Thursday.

But the Welshman – who clawed his way back into the contest with a then outright tournament-best break of 143 – won three successive frames to lead his fellow veteran 5-4.

O’Sullivan responded to take the match to a decider but Williams held his nerve with another century to set up a semi-final against Jack Lisowski, who beat Hossein Vafaei 6-4 later in the day.

“The first three frames I didn’t have a shot,” Williams told the BBC after ending a run of six successive defeats to O’Sullivan, stretching back to the 2014 International Championship in China.

“He tied me up in knots, he was making breaks galore.

“But I felt the crowd started to sway towards me at the end and most of them wanted me to win, which was unbelievable.”

Asked if it was his most satisfying win in recent seasons, the 47-year-old three-time world champion said: “Yes, you’re playing the greatest player ever… and I don’t think I’ve beaten him in the UK for 20 years.

“That’s gone now. If I don’t beat him for another 20 years I couldn’t care.”

Second seed O’Sullivan seized early control with a break of 115 and doubled his advantage in an attritional, 36-minute second frame.

Williams was punished for missing a risky red with the rest in the third frame as O’Sullivan compiled a decisive break of 79 but the contest began to turn before the interval.

O’Sullivan, among the balls and ahead in the fourth frame, chose to wait until disturbing a pack of reds and completely missed them.

Cazoo Masters 2023 – Day Five – Alexandra Palace
Ronnie O’Sullivan reacts during his 6-5 defeat to Mark Williams at Alexandra Palace (Bradley Collyer/PA)

Williams capitalised with a frame-winning 55 and, with the help of a wonderful underarm shot, followed up with 83 in the next.

O’Sullivan’s safety play helped him into a 4-2 lead, but Williams then produced a stunning 143 clearance – his best break at the Masters.

Another fluent 90 levelled the scores and, when O’Sullivan missed a dangerous red into the middle after choosing not to play safe, Williams made a 59 clearance to lead for the first time.

O’Sullivan won a tense 10th frame, making 77 after a long safety exchange, but Williams was not to be denied and made the most of another error from his opponent to build a match-winning 102.

Lisowski also came from behind to edge out Vafaei in a high-quality encounter.

The world number 12 opened in style as runs of 96 and 76 carried him into a 2-0 lead but Vafaei hit back strongly to win the next three, equalling Williams’ tournament-highest break of 143 in the process.

Lisowski levelled after a break of 67 but the next three frames were tightly fought. Lisowski eventually inched 5-4 ahead and then closed out victory with a 74.

“It’s like a dream,” he said. “Three or four years ago I couldn’t win a game here but now to be in the semi-finals feels amazing.”