Derby boss Wayne Rooney branded the challenge that saw Tom Lawrence sent off in the relegation battle with Peterborough as “stupid.”
The Wales international received a straight red card for a lunge on Nathan Thompson although Louie Sibley got him out of trouble with an added-time winner in the 1-0 Sky Bet Championship victory.
There had been few clear chances in the game after Lawrence forced Steven Benda into action in the 11th minute.
Peterborough had to soak up pressure and were reduced to 10 men in the 35th minute when Hayden Coulson was sent off for two yellow cards in the space of four minutes.
But Derby’s numerical advantage was cancelled out two minutes into the second half when Lawrence was shown a straight red for a late lunge on Thompson.
Derby still looked the team likely to score and should have gone ahead in the 63rd minute when Festy Ebosele’s low cross reached Craig Forsyth at the back post but he skied his effort over.
They went close again in the 74th minute when a Jason Knight cross came off Luke Plange and hit the foot off a post but Benda just stopped the ball going over the line.
But Peterborough’s hearts were broken two minutes into added time when Sibley drove a cross-shot past Benda from the left-hand edge of the box.
But Derby must now do without Lawrence for three matches and Rooney had little sympathy.
The Derby manager said: “It’s stupid, it’s a stupid tackle from him and he knows that. He’s reacted, I think he got a bang to his head.
“I’ve said to him he’s very lucky he’s got a manager who understands the situation because I’ve done it many times myself.
“But it’s disappointing and we lose him for three games now although it’s a chance for somebody else to come in.
“We’ve had to deal with a lot of issues this season and it’s another one. He’s our captain and has been great for us but he’ll miss the next three games so if we can pick up some good results it could work well for us and for him in getting some freshness back in his legs.
“We knew it was a big game for both teams and I felt we were better in every department.”
Peterborough manager Darren Ferguson admitted: “It’s a tough one to take so you can imagine how we’re all feeling in the dressing room after putting so much into the game.
“But sometimes as a manager all you ask of your players is to give everything and no one can doubt that set of players gave everything today.
“A week that we felt was going to be pivotal towards the season to only get one point from it is very disappointing.”
Peterborough have gone five games without a goal and Ferguson said: “It’s a huge concern. the amount of shots we had and the shots on target are nowhere near enough.
“We are lacking in quality in really getting a foothold in the game, not heart or desire or effort but just pure quality.
“It’s tough for the lads, we’ve only three players in the whole squad who’ve played any sort of Championship football so it was always going to be tough and so it’s proven.”
