Joe Perry will take a two-frame lead into the final session of his Dafabet World Championship second-round match against defending champion Ronnie O'Sullivan at the Crucible Theatre on Saturday.
The pair shared the eight frames of an absorbing Friday afternoon session as world number 15 Perry moved from a 5-3 first session advantage to a 9-7 lead.
The damage could have been worse for O'Sullivan, with Perry missing a number of opportunities to establish a four-frame lead in the final frame of the session.
Five-time world champion O'Sullivan had made a statement of intent from the start of Friday's session as he compiled a break of 93 in the opening frame, only denied a century by going in-off on the black.
But the unflappable Perry restored his two-frame advantage with a break of 68 and went further ahead with runs of 48 and 46 in the 11th frame.
A missed red by Perry let O'Sullivan in for a break of 66 as he narrowed the gap to 7-5, and O'Sullivan got the better of a safety exchange to move within one frame of his opponent.
But just when it seemed O'Sullivan had hauled his way back into contention, Perry responded with two flawless back-to-back frames, a nerveless 86 restoring his two-frame advantage and a 73 moving him further ahead.
Despite his superb performance, Perry will have been disappointed not to hold a 10-6 lead overnight, with O'Sullivan bringing an end to a lengthy frame and an engrossing session by clearing from yellow to pink.
Ali Carter edged the final two frames of the morning session to give himself hope of overhauling Mark Selby as they prepared to resume their second-round match on Friday evening.
Two-time world runner-up Carter trailed 9-7 after mounting a crucial comeback at the end of a fascinating if scrappy session.
Barry Hawkins let slip a 3-0 lead as he finished tied at 4-4 with Ricky Walden after the first session of what was a repeat of last year's unlikely semi-final.