He admitted: “Yes, it’s a red card. When you see the goalkeeper’s position with his body and his feet, he has made the decision that he is going to dive and catch the ball.
“What he has done is prevent the Hamilton striker from getting an opportunity to score.
“He has caught the ball outside the box and I think it’s a red card.”
Smith also believed Garner, who came on as a second-half substitute, should have been ordered off, too.
Beaton and his assistant had a good view of the 55th-minute incident as the former Preston player had a swipe at Accies midfielder Imrie on the touchline.
It looked a straight red card as Garner. who went on to notch a hat-trick in his side’s 6-0 win, laughed at the stricken opponent.
Smith branded it an act of “stupidity” from the forward.
He said: “It’s a silly challenge. For him not to get ordered off, it’s the strangest thing.
“When you look at the game overall, Rangers (sic) deserved to win and in the manner in which they did.
“But they could have left themselves in a very awkward circumstance.
“It was just stupidity and could have cost them dearly.”
Beaton will be assisted by Alan Mulvanny and Dougie Potter while the fourth official is Bobby Madden, who refereed the last Premiership meeting between the pair.
It was Madden, of course, who refused a stonewall penalty claim in the fading moments of the 1-1 draw when Clint Hill chopped down Leigh Griffiths just as the Hoops hitman was about to pull the trigger.