Trailing by four frames from the first day, the world No 3 halved that deficit and at 9-7 in Hendry's favour, the match could go either way. What is certain is that if the two frames today match the ones that have preceded them, it will be a magnificent prelude to the final.
When O'Sullivan does take off he flies at an altitude that even the likes of Hendry and John Higgins cannot emulate. "It's like a stroll in the park," he says of his sublime moods, and he was thinking of times like his start yesterday.
In the first session of the match Hendry had piled 325 points on to his opponent before he potted a ball, but yesterday it was the six-times champion who had to sit in his chair and watch in horrified wonder as ball after ball thumped into the pockets.
Behind 6-2 overnight, O'Sullivan began with a break of 67 to win the first frame of the day, but that was just the prelude to the fusillade. A 135 followed a 122 and at one point he had compiled 405 points without reply. When he took the fourth, 67-24, he had unpicked all Hendry's good work of the day before.
Hendry had to wait until this storm had blown itself out and he was helped by an interval which allowed him time to regroup and rethink. A break of 57 pushed the Scot into the lead again and although O'Sullivan made it 7-7, he pushed on again with a 45 and a 66 to give himself a narrow advantage.
Earlier there had been a disruption to Higgins' semi-final with Mark Williams that entered the realms of surreal. Snooker has been halted by a wasp before and at the German Masters this season the players had to endure fireworks exploding above them, but rain stopped play? Surely not.
Well almost. With Sheffield basking in glorious sunshine, water started dripping onto the table, which was a nuisance not only because the players find it hard to cue while holding an umbrella but because moisture affects the performance of the balls.
Twenty-six years ago the world championships ground to a halt when the roof began to leak, but that was in Manchester, where they expect that sort of thing. The weather outside confirmed there was nothing wrong with the Crucible's superstructure and eventually the fault was traced to either the lighting or the BBC's above-table camera.
It was Higgins, trailing 5-3 overnight, who first realised something was wrong during the 10th frame. He was on his way to a century break when he spotted a mystery droplet had fallen between the pink and black spots. He tried to dab the liquid away and then called in the referee, Alan Chamberlain.
They failed to clear up the damp spot and things took on an element of farce while table fitter Andy Kennedy started working at the baize with a tea-towel. Higgins briefly played on to complete a break of 104 before the players left the arena and returned to their dressing-rooms.
n Colin Brinded, of Great Yarmouth, is to referee Sunday and Monday's World Championship final for the first time.Reuse content