Darren Ferguson would not blame Lee Tomlin's early sending-off for Peterborough's 4-2 defeat at Ashton Gate.
Posh began slowly and were already trailing to Paul Anderson's opener when Tomlin was shown an 11th minute red card for felling defender Greg Cunningham with an outstretched arm.
"I'm not going to blame the sending-off of Lee Tomlin for our defeat. We cannot start games as poorly as that and expect to get anything," Ferguson said.
"I don't think Lee intentionally used his elbow on an opponent, but if you raise an arm you take a risk and we will now lose him for three games. That is a big blow because he has been in good form. But Bristol started really brightly and it was the goals we conceded, rather than the red card, which cost us."
City led after five minutes when Sam Baldock crossed for Anderson to head in, but after Tomlin's dismissal, a weak header from Cunningham saw City keeper Tom Heaton bring down George Boyd for a 19th minute penalty.
Grant McCann made no mistake with a low spot-kick and Peterborough were back in the game. The home side missed several chances before Baldock restored their lead after 37 minutes, firing past Bobby Olejnik after a neat one-two with Anderson.
The killer third goal came just before the hour mark, with Stephen McManus heading home an Albert Adomah corner. Baldock made it 4-1 from the spot three minutes later after a foul by Michael Bostwick on Anderson.
Dwight Gayle netted a Peterborough consolation with a low 89th minute shot, but City emerged worthy winners, with Baldock and the impressive Jon Stead denied by the woodwork.
Bristol City boss Derek McInnes said: "We owed our home fans a big performance and that's what we gave them. We were the better team apart from a five or ten minute spell after the sending-off, which seemed to affect us more than them.
"We were positive is all aspects of our play and it was a huge result for us. The sending-off made it difficult for Peterborough, but we were already on top at that point."