Peter Ebdon's defence of his Embassy World Championship title hangs in the balance after another tense session with Paul Hunter in Sheffield today.
The world number three is trying to become the only first-time winner of the title to defend the trophy.
But after 16 frames with his Leeds-based rival, the pair cannot be separated.
Three times Ebdon opened up a two-frame lead against first-timequarter-finalist Hunter during today's second session after starting the day at 4-4.
However, each time the Yorkshireman fought back, including a couple of vital frames at the end.
Hunter followed up an 11th-frame break of 120 with 128 to trim his arrears to 8-7.
And he eventually nicked the 16th frame on the pink after a couple of vital misses by the world champion.
Ebdon missed a black on a break of 41 and then later failed to pot the last green with a chance to take a 9-7 lead.
The pair face nine more frames tonight to find a winner to meet Ken Doherty or John Higgins in the last four. The Dubliner is currently 11-7 ahead relinquishing a 10-0 lead.
Mark Williams earlier became only the second player to return to number one in the world rankings.
Williams is the new number one after his clinical 13-7 victory over friend and rival Stephen Hendry.
Stephen Lee, the world number seven, or Hong Kong's Marco Fu stand inWilliams' way as he chases a triple crown.