England Under-21 midfielder Craig Gardner gave Villa the lead with a fierce strike from inside the area.
Midfielder Steve Sidwell scored the opener on 15 minutes after Neil Sullivan had saved from Craig Gardner.
Davies will emulate midfielder Craig Gardner and defender Liam Ridgewell as former Villa players plying their trade across the city.
Birmingham's Craig Gardner was sent off for going over the top as he tried to tackle Franco Di Santo late on.
Reina pulled off superb reaction saves to keep out firm headers from Cameron Jerome and Craig Gardner as the Reds struggled to cope with the home side.
First Fahey headed wide when Shay Given missed Craig Gardner's cross and the Dublin-born midfielder also saw his low shot kept out by the Manchester City keeper.
Craig Gardner brought a fine fingertip save from Steve Harper before Villa took the lead seven minutes before the interval, helped by a liberal sprinkling of good fortune.
When they did get a sight of goal Craig Gardner, who had latched on to a Bowyer lay-off, could only send a shot from the edge of the box high and wide.
Craig Gardner's dismissal against Wigan in September is the Blues' only red card of the season, although they are in a lowly 18th place in the most recent edition of the Premier League's Fair Play Table.
Bowyer, only selected because of an ankle injury to Craig Gardner, was afforded the freedom of the penalty box on 17 minutes and the 33-year-old rolled back the years to burst through and coolly slot past Cech.
After Craig Gardner dragged a free-kick wide and Cameron Jerome's header was cleared off the line by Sears, the Blues got the goal their improvement warranted as Ridgewell beat Winston Reid to a corner and thumped in a header to send the travelling fans wild.
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