Former Villa defender Ridgewell scored an own goal but then only a goalline clearance from Agbonlahor prevented him from putting Blues in front in the closing stages of the derby after Mikael Forssell had headed the equaliser.
Then, within 60 seconds, Agbonlahor was Ridgewell's tormentor at the other end when he headed home an 87th-minute cross from Ashley Young to settle the Barclays Premier League contest.
Agbonlahor consoled Ridgewell and admitted: "I felt sorry for him. He scored the own goal and then I blocked his header off the line before scoring the winner.
"I thought he did well and had a good game. He might take me off his Christmas card list! I'll have to find out if he is still talking to me."
Agbonlahor added: "Being a local lad, it means a lot to me to score in the derby but it was a great overall performance from the lads.
"It is nice scoring against an arch-rival but the most important thing is we won the game and the character we showed will stand us in good stead for the rest of the season.
"When you are 1-0 up away from home, and the home team equalises, your heads can go down and it is credit to the lads that they really kept fighting on.
"We battled on to the end. That is the first away win of the season and hopefully we can start pushing on away from home because at the moment our home form is really good."