Hart, now widely recognised as England's number one, was involved in a mix-up with Kolo Toure that led to Rovers taking the lead in Saturday's Premier League clash at Eastlands.
The pair failed to cut out a long ball from Morten Gamst Pedersen and Nikola Kalinic was left with an open goal in the 24th minute.
City responded and equalised in the 55th minute through Patrick Vieira following a neat one-two with Carlos Tevez.
Blackburn then put up the shutters, leaving Mancini frustrated especially as his side had lost to Sunderland in their previous outing.
However after the 1-1 draw the Italian felt it improper to accuse either Hart or Toure for the goal. "It was a strange goal, " he said. "It can happen. This is football. Joe Hart is a good goalkeeper."
In contrast Paul Robinson, recently retired from England, was in commanding form between the posts for Blackburn.
But although he made a string of fine saves manager Sam Allardyce gave a modest appraisal of the goalkeeper's qualities.
Allardyce said: "Paul has played better than that for us. He put himself in the right position to make those saves today. That has helped us get a point."
He was, however, thrilled at the way his team remained committed to the cause especially as Ryan Nelsen (foot) and Michel Salgado (thigh) came off in the first half with injuries.
Allardyce said: "We have measured up to a club that should brushing us aside in terms of the quality of players they can afford, the wages they can pay and the limited budget we work on.
"But good organisation, team spirit and hard working side can always cause an upset. Manchester City fans would see this result as an upset.
"Even towards the end we might have nicked another goal when Kalinic was through but Joe Hart made a good save. But hopefully this will boost our confidence.
"I was very pleased with our performance. We feel we got what we deserved after an outstanding team effort both in the way we defended and our possession of the ball.
"Nikola capitalised on their mistake and we were pleased he tucked that one away and put us in front. It was an unexpected opportunity to score.
"We looked very comfortable in the first half. I was disappointed Mame Diouf did not make it 2-0. That would have been an outstanding situation for us."
City dominated the match and had the majority of possession but again lacked a cutting edge and Mancini was at a loss to explain why they had dropped two points.
The only positive note came when Vieira scored his second goal for the club following his move from Inter Milan in the January transfer window.
Skipper Tevez shrugged off an ankle injury sustained in midweek when he played for Argentina to resume domestic duties.
But his touch in front of goal let him down and Mancini added: "It was very difficult for him as he only arrived the day before the game. But I still thought he had a good match.
"We were very unlucky. We must have had 25 chances to score against Blackburn. It is very hard when teams put 10 players behind the ball but we have to try and find a solution."