Villa were down a brace through Shane Long and it looked an uphill struggle for the club. The second half saw the Villans burst to life. Three goals within 12 minutes. Ashley Young and Carew with a couple of goals gave Villa the lead but Reading came close on a couple of occasions to tie the match.
In stoppage time Carew was brought down by Ivar Ingimarsson in the box for a penalty. He duly converted it bringing his hat trick dream to fruition.
Villa's win brings to an end, Martin O' Neill's bizarre statistic of not winning a single match in March since his takeover from David O'Leary almost four years ago.
Villa now meet Chelsea at Wembley for the first FA Cup semi-final. Portsmouth awaits the winner of the Fulham vs Tottenham replay.