The home side had raced into a 3-0 lead inside 30 minutes only for Motherwell to haul themselves level on the back of a James McFadden brace but Ojamaa was ordered off before Billy McKay pounced to clinch it.
The Estonian was booked for diving before a late lunge on Andrew Shinnie curtailed his afternoon.
McCall, whose side still need a point to make sure of second place, said: "Henrik knows my opinion on that. It was a dive, he had no need to do it, and it's something we don't enjoy seeing.
"The second one was just a free-kick. That's how Henrik plays, he gives his all.
"I could tell by his reaction that he dived but he looked to be going in on goal.
"Henrik knows how we feel about it and we weren't happy with that but he's a young lad and he has to learn. He has been terrific for us this season.
"But it's a really sore one to take because when Faddy's goal went in just before half-time, I felt we could go on to win it."