Ronnie O'Sullivan gained the early initiative by moving into a 5-3 lead in his Embassy World Championships semi-final Stephen Hendry at The Crucible.
Defending champion O'Sullivan won the final two frames of a tense opening session with seven-time winner Hendry to edge ahead.
O'Sullivan had lit the touchpaper before the best-of-33 frame contest by launching a scathing attack on Hendry in a dispute stretching back to the 1999 world semi-final meeting between the pair.
O’Sullivan was far from happy after being called for a miss and then Hendry insisted he play the shot again. O'Sullivan claimed that, as a result of that incident, Hendry "had gone down in my estimation" and that he had "lost a lot of respect for him".
O'Sullivan and Hendry did at least maintain the appropriate etiquette by shaking hands before the last-four showdown which is scheduled to span three days and four sessions.
O'Sullivan, an odds-on favourite with the bookmakers to reach the final, began in impressive fashion with a break of 115 to take the opening frame.
Hendry levelled in the next with the aid of a run of 33 but O'Sullivan, helped by a fluked black into the centre pocket, edged back in front in frame three.
The final frame before the mid-session interval was a more dramatic affair with Hendry opening up with a break of 65 but then missing a straightforward red into the centre pocket.
O'Sullivan responded with a 63 but left himself a difficult final black which he over-cut after leaving himself too straight on the pink to gain good position.
Up stepped a relieved Hendry to level for a second time.
The first two frames after the resumption were also shared. Sullivan went ahead for the third time after completing a 37 clearance only for Hendry to again respond with a run of 73 to the pink.
But Hendry failed to pot a ball in the final two frames as breaks of 63 in the seventh and 99 in the eighth put O'Sullivan in control.