Ronnie O'Sullivan remains on track for a record-equalling fifth Welsh Open title after easing into the quarter-finals with victory over Zhou Yuelong.

The reigning world champion, who defeated Martin Gould in round three earlier on Thursday, dropped his first frame of the tournament against the Chinese player but was still a comfortable 4-1 winner.

Ali Carter awaits O'Sullivan in the last eight at Celtic Manor in Newport after he defeated Mark Allen 4-2, having earlier knocked out John Higgins 4-3.

O'Sullivan, who is looking to emulate Higgins' five titles in the ranking event, registered breaks of 67, 64, 89 and 74 against Zhou, despite being below his best.

"I got a bit of luck in the safety early on in the game but you are due a bit of luck sometimes," he told Eurosport.

"Even when you are playing bad, you think 'I have to try and win every frame in one visit' - it's just a normal mindset for any top player.

"At the end of the day, it's how good your bad game is. If I can just get my bad game to be a little bit higher - you can't play well all of the time - it keeps me in the game a little bit longer."

Defending champion Shaun Murphy is still in contention to retain the title after holding off a fightback from Barry Hawkins to scrape through 4-3.

Murphy, who led 3-1, trailed in the deciding frame before producing a superb clearance to edge into the last eight, where he will face Stephen Maguire.

Maguire recovered from two frames down to defeat China's Pang Junxu, posting breaks of 105 and 97 en route to a 4-2 success.

Iranian player Hossein Vafaei, who shocked world number one Judd Trump in round three earlier on Thursday, was unable to repeat the trick against three-time world champion Mark Williams, losing 4-2.

Tom Ford awaits Welshman Williams in the quarter-finals after he battled back to win 56-47 in his final-frame decider with Jack Lisowski, having knocked out Kyren Wilson in round three.

Elsewhere, Mark Selby beat Masters champion Yan Bingtao 4-2. Selby, the 2008 champion, will play Jordan Brown for a place in the semi-finals after he overcame Mark King 4-3.