O'Sullivan is the oldest player on show in China

World champion and world number one Ronnie O'Sullivan moved into the semi-finals of the Shanghai Masters in China by defeating Mark Williams 5-3.

He will play Stephen Maguire in the semi-finals on Saturday after the Scot saw off the challenge of Ryan Day 5-4.

"I'm the oldest player in the tournament and there are many young and hungry players who can pot better than me," said O'Sullivan.

"But my break-building's there and if I get momentum I can be tough to beat."

O'Sullivan started brightly with breaks of 93 and 87 for a 2-0 lead, before Williams rallied with a run of 45 to reduce the arrears.

He's probably the best player ever Williams on O'Sullivan

But O'Sullivan, who is aiming to become the first player for 15 years to win three consecutive ranking titles, established a 3-1 interval lead with a cool century break in the fourth frame.

Welshman Williams compiled a 55 break to make it 3-2 before O'Sullivan added a break of 106 to restore his two-frame cushion.

A superb 128 break from Williams kept him in the fight, but O'Sullivan finished the job with a nerveless 78 run to progress.

Williams said: "It was an excellent game and it could have gone either way. I played well but Ronnie makes breaks from nowhere.

"He's probably the best player ever. I'm disappointed because I've won a few tournaments in China and if I'd got through the match tonight I could have gone on to win this one."

Glaswegian Maguire, meanwhile, held his nerve to beat Day in a tense final frame decider.

Day led 2-1, but Maguire pocketed breaks of 114 and 64 to keep his hopes of a Chinese double alive having won the China Open last season.

Breaks of 81 and 61 then kept Day, last season's runner-up, in the hunt, but he missed his chance to clinch victory in the decider.