The two had been neck and neck for two sessions so something had to give. The final session produced three fifty plus breaks and four centuries in the seven frames as the match burst into life and provided the fans to a feats of top drawer snooker.
O'Sullivan struck first with a 53 only for Williams to level once more with runs of 53 and 48. Williams who collected his first piece of silverware earlier this month in China has been playing at somewhere near his best.
The Rocket by contrast has had mixed fortunes since taking the opening event of the season in Shanghai but when he is this kind of form he is virtually unstoppable.
A well crafted century, a 104 switching seemlessly between left and right hand put him 10-9 in front and he followed that with a break of 75 to lead by two clear frames for the first time since the fourth frame.
Williams not to be out done responded with his first century of the match, a 115. This only inspired the Chigwell potter who replied with back to back centuries of a 111 and a 106 to seal a place in the quarter-finals. He awaits the winner of the match between Ding Junhui and Shaun Murphy.
Post match reaction
Ronnie O'Sullivan
Managed to string a few decent frames together, to my surprise. I knew I had to find some kind of form and out of sheer panic and desperation, I was trying to bring the cue through and pot a few balls really.
If I didn't I would definately be going home. I wouldn't say it was really flowing, I was still giving every shot a bit of thought. When you're flowing you don't tend to think, it all just happens. Playing in a big match I needed to handle the big match situation. I kicked into a bit of a gear and tried to stay concentrated all the time.
It was nice to get through that game and come through against a top quality player. I've played too many up and down games over the years to get excited about it.
I didn't play well in any of the World titles that I won, a couple of finals I was relieved to get over the line. In a couple of them I couldn't wait for them to be over I was feeling that much pressure out there, unable to perform and make the breaks you want to out there.
I've managed to win most of my tournaments without playing well. I know I can do it but it would be a lot easier on the nerves if I could find a bit of form and a bit of rhythm. It would be nice to keep applying the pressure to the opponent because that makes your job a bit easier. To be fair the last three or four years I've played better than I have in the previous twelve years, so it's not all doom and gloom.
It's a big tournament and we all want to do well. There are a lot of nerves so it's probably difficult to enjoy yourself.
There is no point in getting carried away, I've thrown away a few world titles over the years, I know why but I can't cure it. I can't afford to let myself get confident.
I never underestimate my own ability when I play aright and I fancy my chances against whoever even when they bring their A game. I'd like to play with my good game against everyone else's good game, that's when I want to be the best player.
I still have spells when I lose six or seven frames in a session at the World Championship and you can't afford to do that.
Mark Williams
It was a fantastic match to be involved in. There were a few little nudges that didn't go my way, and if they had it could have been a different story.
In all honesty though the way Ronnie played, he deserved to get those little nudges and flicks because he played great.
The two clearances he made from 8-6 down lastnight, I dont think anybody could have done them, especially how easy he made them look. It was incredible.
But he played well all through the match. I would think sometimes I had got him in trouble and he would just produce something special.All you can do is sit there and say well done.
There is nothing wrong with his long game,nobody pots every long ball. But every department of his game is spot on.
In my opinion, the only person who is going to beat Ronnie is himself.
