England's Ronnie O'Sullivan plays a shot against England's Judd Trump during the final session of their World Championship Snooker final match at The Crucible in Sheffield, England on May 2, 2022. (OLI SCARFF / AFP)

LONDON - Mark Williams edged out Ronnie O'Sullivan 6-5 to reach the semifinals at snooker's Masters here on Thursday.

In the first quarterfinal at this year's Masters, Williams came from 3-0 down to beat world No 1 O'Sullivan, who has triumphed seven times in the most prestigious invitational event.

"Overall my form is really good, given my age. I'm not going to improve at this stage of my career," the 47-year-old Williams was quoted by the World Snooker Tour website.

Ronnie O'Sullivan, 47, admitted Mark Williams was the better player on Thursday and deserved to win

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By making two centuries and four more breaks over 50, William took his first win over O'Sullivan since 2014.

O'Sullivan, also 47, admitted Williams was the better player on Thursday and deserved to win.

"I didn't score. I was only making bits and pieces and missed a few easy balls," said O'Sullivan. "You shouldn't win matches at this level when you don't make breaks.

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Williams will meet Jack Lisowski, who defeated Hossein Vafaei of Iran 6-4 later on Thursday.