With Brendan Rodgers’ men leading 1-0 thanks to Leigh Griffiths’ smart turn and finish in the 83rd minute, the Belgian defender opted to berate referee John Beaton for nearly 30 seconds.
With the game about to enter stoppage time, Boyata went to ground under the challenge of St Johnstone striker Chris Kane as the defender went to the clear the ball in the middle of the Celtic half.
As play went on, and Celtic eventually won a free-kick for Kane’s challenge on Mikael Lustig, Boyata was seen shouting and gesturing towards the match official.
Once play had stopped the 27-year-old confronted Beaton, shouting in his face. Despite Beaton’s warning that he was in danger of a red card, plus Scott Brown’s attempted intervention, Boyata continued his verbal lashing towards the referee and was subsequently shown a straight red card.
Prior to Beaton brandishing the red card he had the yellow card in his hand, waiting for Boyata to calm down before showing it.
As per The International Football Association Board’s laws of the game the yellow card would have been issued on the grounds of “dissent by word or action”.
The red card offence was for “using offensive, insulting or abusive language and/or gestures”.
From the footage - the game was shown live on BT Sport - it appears that Beaton allowed Boyata to vent, content to simply book the player. But the Belgian’s persistence appeared to push him towards a red card.
The reaction of both Boyata and his Celtic team-mates suggested he deserved and understood his sending off. The player was heading for the tunnel before Beaton had shown the red card.
On his way off the pitch, Rodgers appeared to have words with his player and did not hold back in his post-match interview.
The Celtic boss said: ““It is a stupid red card. He has got enough opportunities to not get sent off. It was a very emotional game towards the end. Dedryck feels as if he should have got a free-kick and didn’t get it.”
“In fairness to John [Beaton], he gives him a chance not to get the red card. It’s not what we would want, but we move on.”
Former Celtic player Chris Sutton, speaking on BT after the match, called Boyata “idiotic” for the sending off, saying it was “pointless and needless” with the player having a good game.
Boyata has proven his worth to the team in recent weeks following his transfer saga during the summer where he angled for a move, with Fulham keen to take him to the Premier League.
He missed all of Celtic’s failed Champions League qualification campaign, with controversy arising from his omission from the decisive trip to face AEK Athens in the third qualifying round which the team lost 2-1.
At times he has cut a frustrated figure despite his fine form. In the first-half at McDiarmid Park he bawled at fellow centre-back Kristoffer Ajer, with the Norwegian deemed to be on his toes and not offering a good angle for a pass.
The Belgian will now miss the semi-final clash with league leaders Heart of Midlothian.