The five-time world champion struck three centuries in a high-quality final to win the tournament for the second time in three years.
O'Sullivan's 31st ranking victory leaves him only five behind Stephen Hendry's all-time record with January's Masters next in his sights, where he will defend the title.
The 42-year-old, who was beaten by Mark Selby in last year's final in York, went into the second session level at 4-4 with his fellow Englishman Murphy.
O'Sullivan started the evening strongly to forge ahead, only for Murphy to hit back with a fine break of 80.
But from then on it was all O'Sullivan, as he reeled off five straight frames, including runs of 103 and 104.
For years, O'Sullivan and Murphy have had a strained relationship, with sniping from both sides.
Murphy had moved to end any animosity between the two before this match, but the 2008 champion failed to prevent 'The Rocket' from powering to victory.
O'Sullivan pocketed a top prize of £170,000 ($227,543) for his third ranking title of the season, which gave him revenge for his defeat by Murphy in the Champion of Champions final last month.