Ronnie O'Sullivan last won the Masters in 2017Venue: Alexandra Palace, London Dates: 8 January -15 JanuaryCoverage: Watch live on BBC TV and Red Button with uninterrupted coverage on BBC iPlayer, the BBC Sport website and the BBC Sport appSeven-time champion Ronnie O'Sullivan was knocked out in the quarter-finals of the Masters, beaten 6-5 by Mark Williams in a thrilling contest.
Both players turned professional in 1992 and are both 47, but it was Williams who knocked out the world number one and reigning world champion.
O'Sullivan surged 3-0 ahead, but Williams hit back to lead 5-4 and won a dramatic decider.
In the evening session, Hossein Vafaei comes up against Jack Lisowski.
O'Sullivan won the last of his record seven titles in 2017, but was ousted by Williams' brilliant comeback, with the Welshman picking up his first win over his English opponent since 2014 at the International Championship.
It didn't start well, though, as O'Sullivan made breaks of 115 and 79 to take the opening three frames as he threatened to run away with the match.
But two-time winner Williams responded by making 143 - the highest break of the tournament so far - 90 and 59, the latter which he clinched with a clearance after coming to the table 49 points behind.
O'Sullivan forced a decider with a pressure break of 77 and had the chance for victory, but he missed the black off the spot, allowing Williams to claim a memorable victory with a fine break of 102.
Williams said on BBC Two: "In the first three frames I didn't have a shot, he tied me up in knots but I felt the crowd wanted me to win towards the end, that is unbelievable.
"You are playing the greatest player ever, if I don't beat him for another 20 years I don't care. It is up there as my best performance. I fancied beating him."
Williams won the Masters in 1998 and 2003 and, asked if he could win a third, he replied: "I am not going to go that far. I have been playing well for a while and I am over the moon."
O'Sullivan reflected: "I just didn't score, didn't make any breaks and my cue ball wasn't great. I hung in there, the battling qualities forced a decider.
"He played the better snooker and was more clinical. I was happy to get it to five and, when you are not playing well, those blacks can be missed."
It is testament to the longevity and success of both players that they are still competing at the highest level of the sport despite approaching 50 years of age.
Six-time world champion and BBC pundit Steve Davis said: "Savour these matches, they won't be along forever.
"That was a special match between two of the great players, they produced the good. Williams was stronger in the end, but it was close."
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