Kyren Wilson rallied to take five frames in the second session this evening as a crowd returned to the Crucible for the start of the World Championship final.
For the first time since the opening day of the tournament, a strictly-regulated number of fans were allowed into the venue in line with government's easing of lockdown rules.
Both players had fought through dramatic final frame deciders against Mark Selby and Anthony McGill respectively to move one more win away from claiming the £500,000 first prize.
O'Sullivan takes a 10-7 lead going into Sunday's final sessions in the best-of-35 frames final.
Earlier today, Wilson was clearly struggling to settle, and missed a further fine opportunity in the fifth frame when he left the pink hanging over the top pocket.
But a loose response from O'Sullivan handed Wilson a second chance and this time the 28-year-old took full advantage, carving out a break of 63 to reduce the deficit to 3-2.
Both players exchanged blunders early in the sixth frame before O'Sullivan managed to fashion a break of 48 which proved enough to restore his two-frame advantage.
And he belatedly produced his best in the seventh after Wilson saw a pink drift into the bottom left jaws, responding with his first century, a 106 to go further in front.
The final frame of an underwhelming session saw a succession of glaring errors by both players, culminating in Wilson missing a difficult long pink and letting O'Sullivan in to pot the final two colours and go 6-2 up.
When action resumed this evening, O'Sullivan took the first two frames to take a 8-2 lead before Wilson pulled one back with a break of 92.
Wilson, clearly steeled by that fine break, took the next frame 79-53 to make it 8-4 going into the mid-session interval.
Frame 13 went Wilson's way again on a score of 82-25 to make it 8-5, O'Sullivan clearly looking rattled for the first time in the final.
Wilson then made it four frames in-a-row to make it 8-6 but O'Sullivan claimed his first frame in five to make it 9-6.
But Wilson rallied again in the next frame to rattle in a century break and reduce the deficit to 9-7.
O'Sullivan, however, restored his three-frame lead in the pivotal final frame of the session.