In a Tour Championship classic, Ronnie O’Sullivan overcame a furious fightback from Mark Williams to reach the semi-finals in Wales.

Williams, who trailed 5-3 at the half, found something in the tank as he battled back to force a late-night conclusion.

But it wasn’t to be, as O’Sullivan’s brilliance shone through in a tense final set that he won 65-44.

The two all-time greats and heavyweights of the sport strolled into the Venue Cymru in Llandudno, with Williams looking to take advantage of home advantage and advance to the semi-finals.

With that in mind, the Welshman got off to a flying start, capitalising on O’Sullivan’s mistakes to win a tense first frame that lasted half an hour.

Last year’s beaten finalist showed some early nervousness in the second, and although scoring some early points, a missed black – which rocked the jaws of the pocked – gave Williams the opportunity to build again. However, he blew his opportunity, and O’Sullivan was able to tie the game.

O’Sullivan appeared to be in need of a confidence boost, and a fantastic long pot of a red provided him with just that as he edged into the lead.

What followed erased any thoughts of a difficult start, with O’Sullivan putting on a stunning display of ball striking to move 3-1 up at the interval with a break of 131 – the highest of the tournament so far.

The Welshman was disappointed after squandering an opportunity to defeat O’Sullivan for only the second time in 14 ranking tournament matches over the last 20 years.

It was also the fourth time this year that the three-time world champion had lost a match in the deciding frame.

“I could and should have won it,” said Williams, who came back from 47-0 down in the 18th frame to force the decider.

“It was a great game to be involved in. It was nip and tuck all the way to the end, but it’s plain to see when it comes down to the nitty gritty I’m not good enough to close out these matches.”

On Friday, O’Sullivan, who will reclaim the world number one ranking at the end of this week, will meet defending champion Robertson in a rematch of last year’s final.

Judd Trump and Luca Brecel meet in the final quarter-final on Thursday, with the winner facing John Higgins, who defeated Zhao Xintong 10-9.