Ronnie O'Sullivan was threatening to pull away from Ali Carter in the Betfred.com World Championship final.
With one frame remaining of the evening session, firm pre-match favourite O'Sullivan led 10-6 and was putting himself in a strong position to repeat his Crucible triumph over Carter of 2008.
Eighteen frames is the target for the title, with the match due to reach its climax on Monday evening.
O'Sullivan hit a purple patch of form at the end of the opening afternoon session which illustrated the difference between the players. A sprint to 92 was followed by a total clearance of 141 in the final frame as Carter slipped 5-3 behind in their all-Essex tussle.
O'Sullivan has revealed this match could be his last before retiring, and despite making similar claims in the past on several occasions, the prospect of retiring at the pinnacle of the sport, with a fourth world title, holds considerable appeal to the 36-year-old from Chigwell.
The rush of heavy scoring from the firm title favourite was barely in keeping with the action which came before or after it, though, because for much of the opening day the pair were mired in safety exchanges.
A break of 56 steered O'Sullivan ahead in the day's first frame, after the pair spent almost 12 minutes toying with each other before the first red dropped. O'Sullivan's first century, a 117, was triggered by a fine long red and pushed him 2-0 in front.
Carter replied with 84 and it was 2-2 after a battle of the minds in frame four, with every red grouped around a corner pocket. O'Sullivan had the first real chance but spurned it by potting a red when attempting to knock in the black, and Carter seized his opportunity.
They split the next two frames, before O'Sullivan found the form which carried him to earlier wins over Peter Ebdon, Mark Williams, Neil Robertson and Matthew Stevens - three world champions and a two-time runner-up.
On the resumption in the evening, the match frequently returned to its earlier disjointed state, with the safety from both men outstanding at times. O'Sullivan moved 9-5 clear with runs of 49 and 68 and a sprinkling of low breaks. Carter, from Tiptree, cut into the lead with a 59 break, but a swift 62 from O'Sullivan restored the four-frame cushion.