Ronnie O’Sullivan’s World Snooker Championship rival forgot a crucial rule at the worst possible time during the pair’s second-round clash at the Crucible on Saturday. The Rocket was facing Pang Junxu when the Chinese potter was left with egg on his face.

O’Sullivan has enjoyed a stunning return to action following his lengthy hiatus from the table. The seven-time world champion brushed aside Ali Carter in the tournament’s opening round and is in a commanding position against Pang after the opening session.

But it was in the seventh frame of the match where Pang was left scratching his head following the unfortunate gaffe. Pang was gearing up for a shot when the referee intervened to explain to the 25-year-old that the cue ball was touching the black ball.

In this situation, protocol dictates that the player taking the shot must inform the referee which target they are aiming for, as technically it counts as hitting the black first, given the cue ball is touching.

Despite being informed by the match referee, Pang failed to tell the man in the middle which ball he was aiming for, meaning his shot was immediately called as a foul. Pang, somewhat confused, turned to the referee to ask why and was met with the response: “You didn’t declare your colour, I asked you to declare. You have to declare.”

It didn’t prove too costly for Pang, though, given he would return to the table and take the frame. But the day would ultimately belong to O’Sullivan, given the 49-year-old finished the session with a healthy 6-2 lead.

While there is still a mountain to climb for O’Sullivan if he’s to make it eight world titles next month, fellow seasoned professional Jimmy White believes he’s trending in the right direction. Speaking to TNT Sports at the interval, White said: "Pang had a few chances, but Ronnie is 6-2 in front and his day’s work is done. If he was 5-3 or 6-2 up, he would go to dinner tonight and may have thought about missing one or two balls, but is 6-2 in front.

"The motivation is to get to 13 before the other guy. If you are getting ready for a tournament it is perfect, he’s going through the gears nicely."

O’Sullivan and Pang will play to a finish tomorrow [Sunday] afternoon, with the winner set to face either Si Jiahui or Ben Woollaston.