Ronnie O'Sullivan came from two frames down to lead 5-3 in his Tour Championship final against Neil Robertson in Llandudno.
Englishman O'Sullivan, 43, will become world number one for the first time since 2010 and the oldest for 36 years if he goes on to lift the trophy.
He compiled breaks of 74, 97, 71 and 67 in consecutive frames to move 4-2 up.
The world number two edged a narrow seventh frame but Australian Robertson battled to take the final frame.
They resume on Sunday at 13:00 GMT, with the first to 13 winning £150,000.
Current world number two O'Sullivan will replace Mark Selby in the top spot if he triumphs.
Welshman Ray Reardon was a world number one aged 50 in 1983.