Edinburgh head coach Michael Bradley was confused by referee Peter Allan's decision to show Matt Scott a yellow card moments before Moray Low scored the only try to give Glasgow a 17-12 RaboDirect PRO12 victory at Firhill.
Home stand-off Duncan Weir and opposite number Phil Godman had kicked three penalties apiece before Scott was penalised for a dangerous tackle on Robert Harley in the 68th minute. With Edinburgh a man down, Low drove over after a lineout a minute later to help Glasgow to victory, which also saw them retain the 1872 Cup.
Referee Allan only made the decision on the advice of assistant Andy Macpherson, and Bradley said: "It was a crucial decision in the game. We have had a lot of possession for all of the game. The yellow card was decisive in terms of the balance of power."
He added: "The referee was next to it and didn't seem to put his hand in his pocket or stop the play even, and the touch judge saw what he saw."
Glasgow head coach Sean Lineen did not feel the incident was so important.
"The subs made a difference," said Lineen, who brought on the likes of John Barclay and Scott Wight after the visitors had cancelled out Glasgow's 9-3 half-time lead.
"They upped the tempo and we got some quick ball. Matt Scott, a centre, was the one who was yellow-carded. I don't think he would have done anything with the drive."
Lineen, whose team were watched by a record 8,852 crowd at Firhill, added: "It's a shame we couldn't put on a better performance for the purist but in a derby match, winning is all important."
Bradley was encouraged by his team's performance after making 13 changes to the team that drew 23-23 with Glasgow on Boxing Day at Murrayfield.
"I thought we played particularly well," he said. "Even when down to 14 men Jonesy (Lee Jones) was almost down in the corner."