A lady wearing a lilac cardigan and a red bag across her shoulder broke free from the stands in Barnsley before storming on to the main stage.
She proceeded to run round the table as O’Sullivan, who was 3-1 up against Zhang Anda, played on – potting the pink to take his break to 129.
Her antics left the crowd in stitches while Eurosport commentator Neal Foulds said: “He’s going to play on, but I don’t know what she’s doing. I’m not sure how she got in past security, frankly.”
Security then try to usher her away only for O’Sullivan to offer her his cue.
It led to whoops and cheers from the English Open crowd as she got down to play the black.
A bemused Foulds said: “He’s going to let her pot the black – or have a go at it.”
O’Sullivan then cranes his head to watch the intruder play her shot – and she sets up relatively well to make it.
Before playing it, she jokes ‘do I get money if I get it in’, but she overcuts it and misses.
Security then try to usher her away again only for the woman to have a second shot at the black, which she misses again. She was then whisked away by tournament security.
O’Sullivan, speaking on TV about the incident after, said: “I didn’t know what to do at first. She said to me ‘I’m just having a jog’.
“I was like ‘go on then, carry on, I’ll play another shot while you’re at it’.
“I thought she was going to pot it. I really wanted her to pot it.
“I thought one of the security guys was going to rugby tackle her – it would have killed her! I saved her from getting rugby tackled!”