LONDON - Ronnie O'Sullivan makes his Crucible entrance on Monday but the appealing prospect of his clash of styles with Peter Ebdon has been overshadowed by a row sparked by Mark Allen.

Allen, the 26-year-old Antrim player, last night bowed out of the Betfred.com World Championship and accused his surprise conqueror Cao Yupeng of failing to own up to a "blatant" push shot in frame 10, at a pivotal stage in the match.

After losing 10-6 to the world number 81, Allen said he was "disgusted" with the behaviour of his 21-year-old Chinese opponent, who was making his debut in the tournament and was later shocked to learn of the accusation against him.

Allen then questioned the sportsmanship of Chinese players in general - sure to go down badly in the nation where snooker is a boom sport, hosting many major tournaments, and where he has already caused offence this season, after branding the island of Hainan, which staged the World Open, as "horrendous" and its people as "ignorant". Allen went on to win that tournament last month, but he may not be welcomed back to China.

Allen said at his post-match press conference yesterday: "I thought the big turning point in the match was at 5-4 when he was in the balls and Paul Collier, the referee, missed a blatant push.

"It was quite obvious to me and anyone who was watching at home would have been able to see it."

There is no rule covering the issue but players are expected to call fouls which are not spotted by referees. Allen clearly thought Cao would speak up.

Allen added: "It seems to be a bit of a trait for the Chinese players because there've been instances in the past, of fouls and blatant cheating going on. It needs to be corrected.

"I'm disgusted that it happened. It shouldn't happen in professional sport."

Cao was asked if he remembered the incident, but said, through a translator: "I was just focusing on playing. I didn't realise if I had fouled. If I fouled, I say sorry. If I didn't foul, and Mark said that, then I would feel very upset and angry."

Allen's comments are to be closely examined by the World Professional Billiards and Snooker Association.

O'Sullivan begins his bid for a fourth world title when he tackles Ebdon this afternoon, seven years since the pair last went head to head in Sheffield. That proved to be one of the most famous matches the tournament has ever known, with Ebdon coming from 8-2 behind to win, frustrating O'Sullivan with his slow play.

Former world champions Stephen Hendry and Neil Robertson reached the second round, both posting 10-4 wins, Hendry against Stuart Bingham and Robertson against 1997 Crucible king Ken Doherty.

Seven-time winner Hendry faces an all-Scottish battle with four-time champion John Higgins at the end of the week, the first time they will have played each other at the Crucible.

Shaun Murphy held a 5-4 over Welsh debutant Jamie Jones, and 17-year-old Belgian Luca Brecel trailed Scotland's Stephen Maguire 6-3. (PA)