Midfielder Stevenson was shown a straight red card by referee Willie Collum for a 25th-minute challenge on United winger Gary Mackay-Steven which left the Jambos facing an uphill struggle.
Goals from Johnny Russell, Willo Flood and Michael Gardyne made Ngoo's 76th-minute strike a mere consolation.
McGlynn said: "The sending off killed the game, and it was probably a very good game for 25 minutes or so.
"The few people I have spoken to who have seen it on TV think it was harsh. We will have a look at it once we get some video coverage but it didn't help us.
"According to Ryan, the lad [Collum] says that he never touched him but that is the rulebook and he has to go with the rulebook.
"The players feel if you go into a tackle when you are on the ground you can hardly go with your studs on the ground.
"It is hard enough losing a player for an experienced side to cope with but we're not an experienced team.
"We had a lot of young players out there so it was hard going.
"We gave ourselves a chance through Michael Ngoo's goal late on but I can't fault the players too much for their effort."