Ronnie O'Sullivan fell behind in the Dafabet World Championship final as the man he calls "the torturer" had him on the rack.

In a dramatic turnaround at the Crucible, Mark Selby came from 10-7 adrift at the start of play to lead 12-11 heading into the decisive evening session - and O'Sullivan was rocking, his mission to land a sixth world title dealt a huge blow.

Selby had trailed 8-3 and 10-5 during Sunday's opening exchanges, but after taking the last two frames to reduce his overnight arrears he added all four before the mid-session interval on Monday afternoon.

O'Sullivan will know he should have pinched the last frame though, with the champion of the past two years missing the easiest of pinks in the 21st frame, electing for power over precision, that would have secured him a lead.

So attritional was the contest proving that the session was halted two frames early, giving the players a break before the 7pm resumption. With 18 frames the victory target, another of the Crucible's famous late-night finishes appeared a certainty.

O'Sullivan's overnight lead had flattered Selby. To be within striking distance was the very best he could hope for from a shaky performance that followed his thrilling late-night finish against Neil Robertson in the semi-finals on Saturday.

Despite him facing the second World Championship final of his career, it was understandable that 2007 runner-up Selby should be jaded. O'Sullivan, having given himself a day off by beating Barry Hawkins with a session to spare, should arguably have inflicted a savage punishment.

O'Sullivan's advantage was whittled away by Selby, with the 30-year-old from Leicester starting to capitalise on the opportunities he had previously been repeatedly squandering.

The last thing Selby needed midway through the final was an interrupted night's sleep, but a 3am fire alarm at his hotel meant that was the case.

Yet it did not appear to affect him in the slightest as he bludgeoned his way through the three frames that launched the final day of the 17-day tournament.

A run of 55 guided him to the opener, followed by 52 in the next - after Selby had begun the frame by giving away 22 points in fouls when O'Sullivan pinned him behind the green from the break-off shot.

When Selby got back to 10-10 with a 74 break it was the first time they had been level since the start of the match. O'Sullivan's display was error-ridden, a world away from the clinical cueing that brought him rapid-fire wins over Hawkins and Shaun Murphy earlier in the tournament.

And when Selby hacked his way through another long frame, the audience could hardly believe their eyes, the champion being tamed and made to look ordinary.

It was a stilted affair, defined by one safety exchange after another, and the run of the balls was favouring Selby. If there was a fortunate nudge going, it was Selby who was benefiting.

O'Sullivan drew level after finally finding some fluent potting on the way to 50 in the 23rd frame, and after drawing three missed attempts to hit the yellow from Selby to seize the advantage in the last of the truncated session he had the most inviting of chances to secure the lead his play scarcely deserved.

He had a near-straight shot on the pink to the middle pocket, and it was all he required. For reasons obvious only to O'Sullivan he looked to drive the ball in at pace, and it wriggled around the pocket before bouncing out on to the table, unwilling to drop. Selby snaffled the unforeseen chance and clipped in the black under pressure, punching the air with obvious delight to be ahead as the players headed for dinner.

O'Sullivan, who has sports psychiatrist Dr Steve Peters with him, headed to the interval with his prospects of a third consecutive title in the balance.

He credits Peters with turning around his career. It remains to be seen whether the mind doctor can help O'Sullivan, who has never lost in a World Championship final, emerge from his snooker stupor on this occasion.

The finalists were playing for a £300,000 jackpot, with the runner-up due £125,000.