Snooker great Ronnie O'Sullivan is on course for a seventh World Championship title after putting a row with the referee behind him to establish a 12-5 lead over Judd Trump in this year's final on Sunday.
O'Sullivan will need just six more frames for a victory that would equal Stephen Hendry's modern-day record of seven world crowns when the best-of-35 contest is played to a finish at Sheffield's Crucible Theatre on Monday.
Match referee Olivier Marteel accused O'Sullivan, 46, of making an obscene gesture after failing to get out of a snooker in the eighth frame.
That led O'Sullivan to challenge Marteel by telling the Belgian official he "saw nothing".
O'Sullivan, who had been 5-1 up, lost the next two frames to 2019 world champion Trump and at the end of the session left the arena without offering the traditional handshake to Marteel.
The World Snooker Tour subsequently issued a statement that said: "Ronnie O'Sullivan received a formal warning from the referee following a gesture he made in the eighth frame."
Prior to the snooker authorities' statement, O'Sullivan told Eurosport: "I just think he (Marteel) seems to be looking for trouble."
O'Sullivan quelled any lingering controversy by offering a fist bump to Marteel at the start of the evening's play.
Trump though won his third frame in a row to cut O'Sullivan's lead to 5-4 in an all-English final.
But O'Sullivan, the oldest player to appear the showpiece match since mentor Ray Reardon in 1982, hit back with a break of 66.
He then capitalised on a succession of errors from a clearly nervous Trump, with the 32-year-old left-hander having said beforehand it had always been a "dream" to play boyhood hero O'Sullivan in a world final.
Trump missed a simple black in the 11th frame and O'Sullivan punished him with a break of 118, his third century of the match.
It was a similar story in the next when, after Trump missed another seeingly routine black, O'Sullivan's clearance of 97 put him 8-4 ahead at the mid-session interval.
Trump, a renowned long potter, then missed with an effort to the bottom corner when play resumed and O'Sullivan's break of 42 extended his lead.
There were signs Trump might be finding his form in the next only for a missed pink to the middle pocket to let O'Sullivan back in.
A fine safety shot from O'Sullivan led to another missed long pot by Trump and it was not long before he was six frames ahead.
Trump then produced a commendable break of 80 to reduce O'Sullivan's lead to five frames.
But his luck was out in the next when he potted an excellent long red only for the cue ball to rebound into the opposite bottom corner pocket.
The foul let the relentless O'Sullivan back in with an easy red over the corner that was the starting point for a frame-winning break of 60.
Trump made a promising start to the final frame of the session only to lose position and just fail to pot a long-range brown.
It was the only chance the remorseless O'Sullivan required as he ended the day with a masterful clearance of 87 and a seven-frame overnight lead.