The visitors took the lead when former Sky Blues youngster Jonson Clarke-Harris headed in right on the stroke of half-time and City skipper Carl Baker equalised with a stunning overhead kick after 73 minutes.
But the game's real talking point came before either team had found the back of the net.
Just after the half-hour mark Coventry striker Callum Wilson raced through one-on-one only to be taken out by Oldham goalkeeper Mark Oxley outside the area. Referee Dean Whitestone issued a yellow card for the challenge, much to the dismay of the home crowd.
"It is a sending off," Pressley said. "Callum had breached their back line. He pushed it past the goalkeeper who denied him a clear goal scoring opportunity. It must be a sending off but the referee chose not to take the right course of action.
"I thought we dominated the game and when you do that you have to score more than once - and also keep a clean sheet.
"It was another really good effort but it is a game we have to win.
"There is hardly a game when I can criticise our effort and even a goal down with 25 minutes left they kept doing what we preach to them and they got the goal our play merited. It is just that we deserved to win."