Wishaw's John Higgins is trailing world number one Ronnie O'Sullivan 10-6 at the World Snooker Championship.
The Lanarkshire potter had the game at 4-4 but his opponent - who is a six-time champion - made five half centuries to gain a 9-6 advantage.
Higgins made a few loose shots and it proved costly as his foe managed to make it a four frame advantage at the end of Friday's session.
It was O'Sullivan's 10th frame which provided agony for the 46-year-old, potting the black but seeing his cue ball come off the green into the left middle pocket.
Aiming for his fifth world title, 11 years on from his last at the Crucible, the Wizard of Wishaw will need to complete an impressive turnaround to defeat the world's best player.
He made the last four with a 13-12 win over England's Jack Liswoski, winning a final frame decider to take him one game off the final.
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