The five-time champion is the favourite to lift the trophy at the Crucible, but has said that he is happy just to be playing and is less bothered about winning.
He told BBC Sport: "When you've won it five times and you've won everything else then you don't really get that excited about it. For me I'm just happy to still be playing but nah, I don't get excited like I used to when I was going for one, two, threes and fours. You're just kind of hungry for it.
"I've kind of settled at five. It's not a bad innings and if I can add to that, that's great, but you kind of lose motivation in the end. It's not the same kind of motivation, it's a different kind of motivation. A lot calmer, more relaxed about everything.
"There's no pressure on me to win another one but it would be nice. It's a different type of pressure I suppose."
O'Sullivan will meet Stuart Bingham in the quarter-finals.