The 'Rocket' continued his streak of stunning form to take the win in London with a 10 - 4 finish.
He returned from the mid-session interval with only one more frame needed to land victory.
The frame got off to a noisy start, with one over zealous 'Rocket' fan being ejected from the 1,500 strong crowd.
Selby proved he wasn't going away yet - winning the opening frame.
But the Leicester man only managed the one - with Ronnie clearing up the 14th to take victory.
O'Sullivan - who at one stage had a seven frame lead over Selby - faltered somewhat with only two frames away from the win.
Selby took the 10th and 11th to leave a five-frame gap on 8 - 3.
A couple of errors from O'Sullivan gave him a chance to shine and claw back two key frames.
Both players shared table time during a scrappy 12th - with Selby requiring two snookers to take back the frame lead.
But O'Sullivan managed a fluke side pocket yellow to help secure the frame.
Despite Ronnie's form this week, few expected him to take the Leicester cueman to town, with Selby having got the better of O'Sullivan in final-frame deciders of three of their finals.
An excruciating 10th frame closer went to Selby after inexplicable misses by both players - with O'Sullivan and Selby both missing chances on the winning black.
An unstoppable O'Sullivan finished the opening session 7 - 1 ahead, with Selby only managing one frame.
O'Sullivan had four frames in the bag by the mid-session interval - with scores of 97, 70 and 96 going alongside a scrappy fourth.
Although the break did little to help Mark Selby - with O'Sullivan taking the fifth - he managed to claw back from a whitewash leaving the score 5 - 1.
Earlier this week O'Sullivan wowed the crowd, after a quarter-final whitewash of Ricky Walden was described as one of the greatest ever performances in snooker.
Despite his semi-final win over Stephen Maguire, O'Sullivan wasn't quite his free-flowing best.
But a century break in the final frame ended the match with a flourish.
The 'Rocket' only made a late decision to enter the tournament, despite earning an automatic qualifying place for the event with his Crucible triumph in May.
Sunday's stunning Masters win comes after Ronnie O'Sullivan found top gear in Sheffield - securing his fifth world title.
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