John Higgins overhauled Mark Williams' overnight lead to carry a two frame advantage of his own into tonight's final semi-final.
Welshman Williams resumed 9-7 up at the Crucible, but it was a nervy and error-strewn start to proceedings today from both players as they shared the first four frames before the mid-session interval.
Williams' made the highest break of the session with a 70 to go 10-8 up, but he slipped a frame behind at 12-11 when his errors became costly.
Despite a break of 61 by Williams in the next frame, an in-off allowed the three-time world champion to secure his eighth frame in 10 to leave him in control.
The 36-year-old Scot, eyeing a fourth world crown, will now need just four frames for victory when the pair resume at 7pm tonight.