O'Sullivan and Selby lead
Ronnie O'Sullivan continued his march towards a third successive World Championship title while Mark Selby and Neil Robertson's semi-final was squarely in the balance after the first session.
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O'Sullivan opened up a 6-2 lead over Barry Hawkins and Selby was on course to do likewise against an out-of-sorts Robertson, only for the world number one to add to his historic century of centuries and close to 5-3.
The 'Rocket' has played wonderful snooker to win the last two titles at the Crucible, beating Hawkins in last year's final, and since battling from behind to overcome Joe Perry in round two he has again looked the man to beat this year.
He cruised past Shaun Murphy with a session to spare in his quarter-final and was similarly clinical as he established his authority by sweeping the frames after the mid-session interval against the world number four on Thursday afternoon.
O'Sullivan was quickly into his stride with a 63 to take the opener but he strangely turned down a long-range plant in the second and Hawkins, who had spoken in the build-up about the need to punish any slip from his opponent, was true to his word with a 96.
A 76 followed in the next as Hawkins took the early lead but the roles were reversed in the frame before the interval as Hawkins missed a long red and O'Sullivan cleared well.
The resumption was cagey as both players appeared to struggle with the table, but O'Sullivan set those worries aside to make a frame-winning 80 after Hawkins missed a red with the rest.
Another tricky missed red from Hawkins let O'Sullivan in during the next and though he could only make 30, Hawkins' response was ended on 40 by a kick and O'Sullivan cleared with 39.
A 108 in the next frame made it 5-2 and he potted a superb opening red in the last frame of the session. He broke down on 30 but Hawkins played a poor positional shot on a pink and later missed a simple red, allowing O'Sullivan to win the frame.
The evening's action saw Selby take the opening frame with 65 and he should have added the second after Robertson missed a straight pink.
Selby made 54, including a lovely shot from a pink to develop a red near the middle pocket but missed a relatively simple frame-ball red down the top cushion and had to watch a Robertson clearance featuring excellent pots on the yellow and green.
Robertson went 2-1 ahead after a messy end to frame three but there was no such struggle in the next, as Selby played a good shot to open the pink and converted it into a 133 break to deservedly level.
Robertson had said ahead of the match: "I can't allow myself to get bogged down. I have to play my shots and when I'm playing really well I'm very difficult to beat."
But he missed reds along the top cushion in each of the first two frames back, leaving his highest break of the session at 46 and allowing Selby to steal both frames.
And when Robertson was distracted by a noise from the crowd in the next and missed a simple black off its spot, Selby made 31, set a snooker from which Robertson took four attempts to escape, then knocked in a 72 for a 5-2 advantage.
That guaranteed him the overnight lead but Robertson kept it to just two frames with a 130 to leave the scoreline at 5-3.
Robertson came from 5-1 down to beat Selby 10-7 in December's UK Championship final but does not feel the memory of that result will affect the Leicester cueman.
"He's much stronger mentally than that," he said. "The match is so long I don't think scars or anything like that can have too much of an effect."