The Northern Irishman won the last four frames to beat the world champion in Milton Keynes.
Mark Allen has defended himself after a heated exchange with Ronnie O’Sullivan at the end of their Champion of Champions bout on Thursday.
In what proved to be the final frame of a 6-3 victory for Allen, O’Sullivan initiated a lengthy tirade at his opponent’s apparent movement when he was attempting to take a shot.
O’Sullivan, winner of a sixth World Championship in August, had led the contest 3-2 but a 104 from Allen in the sixth frame, his second century of the match, restored parity in the scores.
The latter duly won the next two as well to establish a two-frame advantage before their extraordinary altercation near the beginning of the ninth frame.
O’Sullivan, who has triumphed in the Champion of Champions three times in the past, launched a verbal attack on Allen, claiming that he had been standing up and walking in his eyeline.
As it turned out, Allen scored a break of 66 to close out the victory and move into the last four where he’ll face world number one Judd Trump.
“Honestly, I think Ronnie just got into his own head,” former Masters champion Allen said immediately after the showdown.
“He was taking forever on shots in the previous frame or frame and a half. I left him touching ball a few times just to play easy safeties and he was taking forever over them.”
“He took two minutes to decide to put me back in one of them, I think he was just looking for an excuse if anything went wrong.
“To accuse me of moving on his shots and standing in his eyeline, he’s just crazy.
“Even the ref (Marcel Eckardt) said, ‘I know you haven’t done anything, but let’s just play the game,’ and that’s all I really needed to hear.
“I knew I hadn’t moved and even if I had moved it would have been by mistake, so when Marcel said that I knew I hadn’t done anything.
“I wasn’t going to back down from Ronnie – he’s a great snooker player, the best ever in my opinion, (but) sometimes he just lets himself down with what he does and what he says, and I wasn’t going to let that go because I knew I was in the right.”
O’Sullivan said: “Sometimes someone is continuously in your eyeline when you are on a shot and he’s moving – maybe I read a bit too much into it – but it seemed like stuff you’d do down at the snooker club when you’re an amateur.”
“It is what it is, but I thought I’m just going to pull you up on it and I’m not going to let it go.
“There’s no hard feelings, Mark played better tonight and he deserved his victory but sometimes you’ve just got to say something and get it out of the way.”
Earlier in the day, Allen fought back from 3-2 behind to overcome tournament debutant Scott Donaldson in a decider with a break of 125.
Allen is competing in this year’s Champion of Champions as one of the highest-ranked top-ups, having not won a trophy in the last twelve months on the circuit.