The match swung this way and that as Milkins won the first two frames but then lost four on the spin, with O’Sullivan knocking in a 142 along the way.
The Milkman stopped the rot but the Rocket looked in a great position at 5-3, before a century (120) from Milkins and claiming the 10th to level the match at 5-5.
Milkins had never beaten O’Sullivan before, other than at the one-frame Shoot Out, and he had two chances early in the deciding frame to take control of it, but failed to do so, notably missing a very straightforward pink.
The world number one then got a chance of his own but lost position, visibly frustrated as he dropped his cue on the table, forced to play safe at 46-24 ahead.
After a missed plant from O’Sullivan, the underdog was afforded one more chance but missed a thin red and the Rocket took advantage and claimed the narrow victory.
O’Sullivan will take on Zhou Yuelong in the quarter-finals after the Chinese star downed John Higgins on the other table on Thursday afternoon and the Rocket will be thinking that he needs to play better than he did on Thursday to beat either man.
‘It’s surprising actually because deciders, I normally play them alright,’ Milkins told the BBC. ‘I played a really poor decider, I could have won that, but to be fair I’m chuffed the way I stuck in there because I’ve rolled over against Ronnie every time.
‘The crowd want to see a good match and I think it was a good match in the end, but it’s just annoying it took me so many frames to settle down. If I was settled down, who knows what would happen but I didn’t play my game at all, really disappointed.’
O’Sullivan said: ‘Rob’s played great the last two years. Improved as a match-player, he’s harder to play now than he ever was, so pleased to get through, but the cue action wasn’t great.’
MORE : Ronnie O’Sullivan says he has been ‘asked to consider his future’ by snooker bosses
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