The confident UK and British Open champion moved from 2-0 and 3-2 down to defeat the Dublin-born Regal Masters title holder in the new Skoda Grand Prix.
O'Sullivan's 5-3 success earned him a quarter-final meeting on Wednesday against either the world No 3 James Wattana or John Higgins, the rising Scot.
'Last season when I won the UK title I was only a kid. But I feel I've grown up more and realise now that snooker's a business. No one gets in my way,' said O'Sullivan.
The Ilford rivals shared the first four frames in only 52 minutes with Doherty, the Grand Prix finalist for the past two seasons, making a break of 111 in the opening frame. O'Sullivan's response was runs of 78 and 90 to make it all square at 2-2. Doherty won the fifth 64-0, but then missed the final green in the sixth frame to establish a 4-2 lead.
Andy Hicks, the former British Under-19 champion, beat the giant-killing Euan Henderson, and now meets Steve Davis in the last eight.
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