Ronnie O'Sullivan finally began to dominate second-round opponent Mark Allen at the Crucible as he secured an overnight lead over the Northern Irishman. Despite an inauspicious start, O'Sullivan is now just four frames from a victory which would see him reach the Betfred.com World Championship quarter-finals.

Allen began the second session level at 4-4, with a possible upset on the cards. They shared the opening six frames but O'Sullivan won the final two frames of the afternoon's session to end the night with a 9-7 lead ahead of tomorrow morning's conclusion.

O'Sullivan made breaks of 107, 46, 60, 93 and 59, while Allen had runs of 108, 70 and 115.Allen had a chance to pinch the 15th frame but went for one ambitious red too many and missed, with O'Sullivan knocking in his frame-winning 59.

A clinching 64 from O'Sullivan in the next gave him breathing space, even if he knows the youthful Allen will be determined to come back into the contest tomorrow.

The pace of the session was a tremendous advert for the sport at a time when the authorities are considering whether a game with just six reds is the best way to attract a new generation of spectators.

Two frames won by O'Sullivan were timed at under nine minutes each, and no frame went beyond 18 minutes. Allen has made three centuries in the match so far to O'Sullivan's one but must effectively win tomorrow's session by 6-3 or better to reach the last eight.

World champion O'Sullivan appeared out of sorts in the early stages of the match on Thursday. The 33-year-old defending champion had been frustrated with his opening performance against Stuart Bingham and gave himself marks of five out of 10.

This display was worse, yet somehow O'Sullivan managed to emerge on level terms at 4-4 with the man from Antrim in the best-of-25-frames clash.

World champion Ronnie O'Sullivan again appeared out of sorts as he began his second-round world championship match against Northern Ireland's Mark Allen.

The 33-year-old defending champion had been frustrated with his opening performance against Stuart Bingham and gave himself marks of five out of 10.

Tonight's display was worse, yet somehow O'Sullivan managed to emerge on level terms at 4-4 with the man from Antrim, with two sessions still to come in the best-of-25-frames clash.

O'Sullivan missed three attempts to pot the blue before getting 20 points on the scoreboard. He should still have pinched the opening frame but missed the final pink, and Allen made the pot required to go 1-0 ahead. Allen, 23, was soon 2-0 up following more erratic play from O'Sullivan.

He was back in front in the third frame but missed a long blue to halt a break of 53. O'Sullivan took advantage, clearing to the pink, before winning the next with a break of 67 to level up at 2-2. He went 3-2 ahead but Allen responded to win a scrappy sixth frame.

Allen stormed into a 4-3 lead with a classy break of 119, however, O'Sullivan responded with 93 in the final frame of the session. They resume tomorrow afternoon and the match will conclude on Saturday.

Stephen Hendry and Ding Junhui were tied at 8-8 after the middle session of their second-round duel. They will play to a conclusion on Friday evening