Mark Selby opened his match with John Higgins with three stunning centuries, while Stephen Hendry fell behind despite a 147.
Four century breaks in first session of Crucible quarter-final
Mark Selby opened up his quarter-final with John Higgins with three scintillating centuries on the bounce, but still only ended the session level at 4-4.
Stephen Hendry hit a sublime maximum 147 in the first session of his match against Shaun Murphy to lead 5-3, but Murphy hit back in the second to lead 9-7 overnight.
Neil Robertson leads Stephen Maguire 5-3 after their first session, while Mark Allen is 9-7 ahead after two sessions against Ryan Day.
Seven-time winner Hendry could not build on his maximum effort earlier in the day, as Murphy showed the form that also made his a Crucible champion.
Murphy started the season is the best way possible with a 137 break that started a run of four consecutive frames to lead 7-5.
Runs of 76, 104 and 80 helped Murphy overturn Hendry's lead, and although the veteran Scot hit back to share the final four frames, Murphy takes a 9-7 advantage into the concluding session on Wednesday.
Rematch
Selby and Higgins battled it out in eight excellent frames of snooker in their quarter-final clash.
The rematch of the 2007 Crucible final was one of the highest-quality sessions of snooker ever witness in Sheffield, with four centuries and a 96 break in eight frames.
Selby joined Higgins as the only two players to hit three consecutive centuries at the Crucible on two separate occasions.
25-year-old Selby missed just one pot as he rattled in breaks of 118, 124 and 117, but Higgins is the ultimate competitor and he hit back with the next four frames.
A 141 from Higgins put him 4-3 up, but Selby responded and look like hitting his fourth century only to break down on 96, but it was enough to end a marvellous session of snooker level at 4-4.
Nip and tuck
Allen and Day fought out a battling session that eventually saw the Northern Irishman lead 9-7, but only after taking the final three frames.
Day recovered from losing the opener and going 6-3 behind to reel off four frames on the run to lead 7-6, with runs of 84, 68 and 70.
The Welshman had to sit in his chair and watch Allen level with a 119, and Ronnie O'Sullivan's conqueror then took the final two frames to lead by two.
Australian Neil Robertson moved into a 5-3 lead against world number two Stephen Maguire after knocking in breaks of 76, 105, 98 and 53.
Maguire was struggling badly in the early stages, perhaps feeling the effects of his gruelling second-round match against Mark King, but a run of 75 in the final frame of the afternoon saw him finish on a high.
