Alex Dyer blamed a "lack of judgement" from Danny Rogers as Kilmarnock were held 1-1 at home by St Mirren.
The goalkeeper, a former Saints loanee, carried the ball over his goal line after clutching a header from team-mate Stuart Findlay in the final seconds to earn Jim Goodwin's side a point.
Danny Whitehall had put Kilmarnock in front with a first-half header.
Dyer said: "Overall this season Danny has done really well for us and it's maybe just a lack of judgement.
"He's maybe caught between whether to punch it or catch it. He went to catch it and then his momentum took him back and the ball went over the line. I'm gutted for him and the team because they played well.
"The game should have been put to bed by half-time. We had enough opportunities and chances to do that. And once you don't do that, it gives them a chance to stay in the game.
"They get an opportunity right at the death and it comes right for them and not for us.
"We played well for the most part so I'm gutted for the players. The lads worked hard and played well. We just should have put it to bed earlier and not give them the chance. But overall we did OK today."
Saints boss Goodwin admitted his team had been fortunate to get a point after a poor performance but insisted there were no doubts that the goal should have stood, despite Rogers' protests.
He said: "I have seen it back and Danny has carried it over the line – there is no doubt about it. I thought someone had pushed him but no one is near him. He is just unfortunate he lost his balance and carried it over the line.
"It didn't look like the goal was going to come and I thought it wasn't our day. It is a good point in the end as we were nowhere near our best. Kilmarnock were excellent in the first half and deserved to get the lead.
"In the second half we were better and moved it quicker. I have to credit the players as it has been a busy three weeks with seven games in it."
