Dundee frontman A-Jay Leitch-Smith insists Tomas Cerny should not have stayed on the park to save his penalty.
Leitch-Smith had already opened the scoring for the dominant Dark Blues when he was fouled by the Jags goalie on 23 minutes.
Instead of handing the ball to nominated taker Sofien Moussa, Leitch-Smith took the spotkick himself and looked on in horror as Cerny stuck out a leg to save his shot.
That was just one of many golden chances missed by Dundee and they were made to suffer for their poor finishing as Thistle grabbed an injury-time goal through substitute Miles Storey to secure a highly-unlikely 2-1 victory.
The decision by referee Euan Anderson to merely book Cerny rather than send him off angered both Dens boss Neil McCann and Leitch-Smith himself.
The on-loan Shrewsbury Town player said: “The keeper should have been sent off as I was clean through on goal.
“I was expecting him to go off as I had gone round him and all I would have had to do was tap it into an empty net.
“So I was expecting a red card.
“I knocked it to the side of him and he has brought me to the floor and that is a clear goalscoring opportunity.”
Manager McCann agreed, saying: “That’s the defining moment (the penalty save).
“I saw the Partick Thistle players going over to him at the end because it was the defining moment.
“I don’t think Cerny makes any attempt to get the ball.
“Now the rules are, if you make a genuine attempt to get the ball it’s a booking.
“There is no attempt there to win the ball – he has cleaned out the player.
“Without doubt I am absolutely fizzing inside because it takes me all my control at the side of the pitch not to lose my rag and get sent to the stand.
“That’s a disgraceful decision.
“There is no attempt (to win the ball), I don’t care what anyone says.
“He should have walked.”
As for the decision to take it himself rather than hand the ball to Moussa, Leitch-Smith added: “If you win the penalty then you want to take it – don’t you?
“The manager mentioned that Moussa should have taken it after the game.
“I tried to wait for the keeper to move and he left his leg there.
“Unfortunately, I missed when I should have scored.”