Ricky Walden won four frames in a row to hold a 5-3 lead over Martin Allen after the first session of their UK Championship semi-final in York.
The Chester man fired centuries of 124 and 127 in a topsy-turvy afternoon at the Barbican Centre.
Allen had raced into a 3-1 lead at the mid-session interval before Walden's fightback.
The winner of the best of 19 frame contest will face Judd Trump in the final after he saw off Neil Robertson 9-7 yesterday.
