Ali Carter holds a 9-7 advantage over five-time champion Ronnie O’Sullivan after the second session of their round two match at the World Snooker Championships in Sheffield ©Getty Images

Ali Carter holds a 9-7 advantage over five-time champion Ronnie O’Sullivan after the second session of their round two match at the World Snooker Championships in Sheffield.

Carter's lead in the all-English encounter had previously stood at 8-3 after he won five frames in a row at the Crucible.

But O'Sullivan won four of the day's last five frames to reduce the deficit to two.

Northern Ireland's Mark Allen earlier became the first player to book his place in the quarter-finals with a 13-8 victory over England's Joe Perry.

The pair started the third and final session tied at 8-8 after Perry, who beat compatriot and reigning champion Mark Selby in the first round, overturned a 5-3 deficit.

But Allen gained control of the match by winning the first four frames of the evening, helped by breaks of 133 and 74, before clinching the match in style with a 122.

Northern Ireland's Mark Allen became the first player to reach the quarter-finals ©Getty Images
Northern Ireland's Mark Allen became the first player to reach the quarter-finals ©Getty Images

Elsewhere, world number six Barry Hawkins of England holds a 9-7 lead over Chinese qualifier Lyu Haotian, who fought back from 8-3 behind to keep himself in the hunt going into the conclusion of the contest tomorrow.

The other afternoon match saw world number nine Kyren Wilson of England earn a 5-3 overnight lead over Welsh qualifier Jamie Jones.

Action in Sheffield is due to continue tomorrow.

The final is scheduled to take place on May 6 and 7.