HE FELT invincible in sealing his fourth world title 12 months ago but defending champion Ronnie O'Sullivan insists he will need to improve if he is to make it five.

The 37-year-old entered the draw as the defending champion and top seed despite having taken the best part of the last year out of the sport on self-imposed exile.

But last night it looked as if he had never been away as he saw off Ali Carter, who he beat in the final a year ago, 13-8 to move into the quarter-finals.

O'Sullivan will now face Stuart Bingham but it was the manner of his destruction of Carter that will have his rivals worried.

The Rocket fired in three century breaks and eight more half centuries in wrapping up the win against Carter.

While his long potting still looks rusty, in and around the balls O'Sullivan is as good as ever - leading many to predict yet another procession to the title for the ambidextrous star.

But he insisted: "I didn't know if I was going to get through the first round, to have got to the quarter-finals is a bonus for me.

"I still believe I will have to up my game to win here. Last year I was playing shots that I thought 'wow', I felt invincible and knew that every time I got in I was going to clear up.

"This year is different because I haven't played any matches, I don't know what my level is. Last year I felt so good that I could have played another 17 days straight after the tournament finished."

O'Sullivan's opponent in the last-eight will be Bingham after the world No.8 found his best snooker at the right time to seal a 13-10 win over Mark Davis.

Bingham, who before this year had never been past the second round at the Crucible, reeled off the last three frames in a row.

In the bottom half of the draw Ding Junhui produced some magnificent snooker as he overcame a 6-3 deficit to seal a 13-9 win over qualifier Mark King.

And King admitted afterwards that playing like that there is no-one, including O'Sullivan, who will be able to live with the Chinese star as the tournament progresses.

"When he's playing like that all you can really do is just sit there and watch, he was hitting the ball so sweetly and is so good in and around the balls," he said.

"I don't think even Ronnie can beat him when he plays like that, I just had to sit there and really admire him."

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