Villa were outclassed early on by the Championship side, who had eliminated Liverpool and Burnley earlier in the tournament, trailing 2-0 at the intermission following a brace from striker Shane Long.
However, O’Neill’s side erupted for four unanswered goals - three coming from the impressive Norwegian - to earn a trip to Wembley for the semi-finals on April 10th, where they will face holders Chelsea.
O’Neill stressed that Carew needs to gain consistency, using this performance as a basis of comparison.
“Gabriel Agbonlahor was poorly this morning and had to go home so John steps in and scores a second-half hat-trick which was absolutely delightful,” O’Neill said.
"John at his hungriest can perform like that.
"Goals give him confidence and the next thing you know he is running the game. He can do that and I want him to perform like that more often.”
Following a first half in which trailed by two goals, Villa awoke, scoring three times in the span of ten minutes to grab the lead on 57 minutes. And the manager was hughly impressed with the fight his team showed.
"It was a great spell by us just after half-time and we needed to do something because we had played so meekly in the first half,” he added.
"I think after all the effort that we have put in both cups this season, to go out as meekly as we might have done would have been very disappointing.
"But I am delighted with the team, we have showed great character.”