Both Priestman and Gordon were judged to have denied a goal-scoring opportunity after Beaton went to the monitor.
And Aston Villa’s 83-times capped McGinn, whose brother Paul captained Motherwell, said on social media: “I’ve sent you to the screen let’s send you to an angle from the North Sea to back it up.
“Scottish var is a mess.”
In his post-match interview, Motherwell manager Jens Berthel Askou told BBC Scotland: “We get Liam Gordon sent off in a decision that is a mystery to me and will remain a mystery to me because there are two players covering behind him who will, without a shadow of a doubt, get in his way or at least make sure it’s never a very obvious goal chance.”
The Scottish FA have been approached for comment.
