O'Sullivan said he had had problems sleeping before the match

A century break inspired Carter to a 3-1 lead, and a break of 92 put him 4-2 up, only for O'Sullivan to pull it back and set up a tie with Marco Fu.

"I was lucky really. I expected Ali to win with the chances he had. He should have put me away," said O'Sullivan.

"He'll be disappointed, but I wasn't playing well. I wasn't very positive."

Fu is the last Asian player left in the tournament after a high-scoring 5-3 win over Matthew Stevens.

Breaks of 62, 57 and 63 saw Fu advance, although Stevens ran up breaks of 61 and 65 himself.

World champion Graeme Dott and last season's Masters champion John Higgins will also meet in the last eight after impressive victories.

Dott managed a break of 118 and three others of over 50 in a 5-1 win over Neil Robertson, one of the form players of the season.

Higgins beat Jimmy White by the same score, with his highest break being 81, while White's best run was just 38.

Barry Hawkins, meanwhile, continued his good form with the first whitewash of the tournament, against Joe Swail.

The Dartford potter, who had not won a match at a ranking event all season before beating Ding Junhui in the first round, ground out a 5-0 win over the Northern Irishman, winning a series of close frames.

"That was an awful performance compared to the way I played yesterday," Hawkins said.

"It was hard to get up for the match after such a big occasion against Ding, but it was a big match for me because I need as many ranking points as I can get."

Hawkins will play Dubliner Ken Doherty in Friday's quarter-finals after the 1997 world champion dispensed with Leicester's Mark Selby 5-1.

Selby pocketed the first frame with a superb 85 break, but Doherty reeled off the next five including breaks of 120 and 56.

"Barry's playing really well, so I'll have to play well to beat him," said Doherty.

The other quarter-final will feature 2005 world champion Shaun Murphy, who beat Stephen Maguire 5-2, and Jamie Cope, who overcame fellow Englishman Stuart Bingham 5-4.

Thursday's second round results:
(best of nine frames)