The five-time world champion was about to put the finishing touches to a 4-1 win over Chinese player Zhang Yong when a middle-aged woman evaded security at the Barnsley Metrodome and began running around the table.
O'Sullivan stayed composed to sink the pink and was one ball away from a total clearance of 136. But rather than pot the black himself he handed his cue to the giddy fan, who was dressed in blue jeans and a grey top and carrying an orange handbag.
"I didn't know what to do at first and she just said, 'I'm just having a jog, I'm just going for a jog'," O'Sullivan told Eurosport.
"And I was like, 'Go on then, carry on then, there's your jog, have a shot as well while you're at it'.
"I thought she was going to pot it. I really wanted her to pot it.
"I thought when the (security) guys came out they were going to rugby tackle her, but I thought, 'If you do that, you might kill her'."
O'Sullivan made earlier breaks of 126 and 127, and he said handing her his cue at the end of the match probably saved her the wrath of security.
"I saved her from getting a rugby tackle," O'Sullivan added.
Later, O'Sullivan crowned a dramatic day with a 4-3 victory over John Higgins.
O'Sullivan won the final two frames against his old rival to reach the quarter-finals.
Neil Robertson was a convincing 4-1 winner Aditya Mehta, having seen off namesake Jimmy earlier in the day, while Michael White followed up a 4-0 victory over Ben Woollaston by beating James Wattana 4-3.
Alexander Ursenbacher provided the biggest upset of the evening as he saw off Shaun Murphy 4-1, despite losing the opener. The Swiss was far too good thereafter, a 123 break in frame four the highlight.
Anthony McGill won two deciding frames to beat first Akani Songsermsawad and then Yan Bingtao, while Hossein Vafaei edged past former world champion Stuart Bingham before an altogether more straightforward 4-1 success against Andrew Higginson.
Xiao Guodong had produced the headline result of the afternoon session, seeing off Mark Selby 4-1, but was unceremoniously dumped out of the event as the evening as Kyren Wilson raced to a 4-0 win.
The headline result of the evening session belonged perhaps to Jack Lisowski, who fought back from 2-1 and 3-2 down to beat Judd Trump 4-3.
Thursday afternoon results
- Anthony McGill 4-3 Akani Songsermsawad (Match 101)
- Aditya Mehta 4-1 Chen Zifan (Match 103)
- Mark Williams 2-4 Jack Lisowski (Match 105)
- Alexander Ursenbacher 4-2 Stuart Carrington (Match 110)
- Hammad Miah 1-4 Andrew Higginson (Match 112)
- Stuart Bingham 3-4 Hossein Vafaei (Match 113)
- Thor Chuan Leong 1-4 Kyren Wilson (Match 114)
- Liang Wenbo 0-4 Yan Bingtao (Match 100)
- Jimmy Robertson 2-4 Neil Robertson (Match 102)
- Zhang Yong 1-4 Ronnie O'Sullivan (Match 106)
- Robert Milkins 3-4 John Higgins (Match 107)
- Michael White 4-0 Ben Woollaston (Match 108)
- James Wattana 4-2 Yuan Sijun (Match 109)
- Liam Highfield 3-4 Shaun Murphy (Match 111)
- Judd Trump 4-1 Matthew Stevens (Match 104)
- Xiao Guodong 4-1 Mark Selby (Match 115)
Thursday evening results
- Ronnie O'Sullivan 4-3 John Higgins
- Neil Robertson 4-1 Aditya Mehta
- Alexander Ursenbacher 4-1 Shaun Murphy
- Michael White 4-3 James Wattana
- Andrew Higginson 1-4 Hossein Vafaei
- Yan Bingtao 3-4 Anthony McGill
- Judd Trump 3-4 Jack Lisowski
- Kyren Wilson 4-0 Xiao Guodong
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