O'Neill, whose side needed a late equaliser from captain Stiliyan Petrov to earn a draw at Selhurst Park, has demanded his players give everything at Villa Park as a quarter-final place goes on the line.
He said: "I don't think the fact we are playing the Carling Cup final on Sunday will affect the players. They will be very much focused on the Palace replay.
"We treat every game on its merit and work accordingly. Obviously we want to be as fresh as possible for Sunday but we don't have a free week before the final.
"The most important issue at the present time is that we want to get through to be playing either West Bromwich Albion or Reading in the quarter-final. That is our aim.
"Crystal Palace will be licking their lips at the prospect of playing us again because they played exceptionally well in the first match and are capable of doing it again.
"For an FA Cup game you can disregard their form leading up to the tie.
"The game I saw them in was against Wolves in which they did exceptionally well and they deserved to win.
"They will be relishing the thought of playing at a Premiership ground simply because it is the FA Cup and they have nothing to lose.
"They will be very determined. It is a big opportunity for them and they will come to Villa without any real fear.
"They have a number of players capable of turning matches but I think it is their togetherness that has been the most important part of their team, certainly in recent weeks because of the administration problems."
Despite having to play an extra game before their trip to the national stadium, O'Neill is just pleased to still be in the FA Cup thanks to Petrov's late heroics.
He thinks the skipper's strike epitomised Villa's never-say-die attitude and added: "Where I have been pleased with the team is that we have come from behind on a number of occasions. We have shown that character to fight back.
"From that viewpoint the players are getting a bit of confidence in themselves and why shouldn't they?
"Being in the FA Cup still means a lot to us and plenty to Crystal Palace as well in every sense. What we want to do is to go out and get in front which we haven't been in the tie and try to see it through."
Villa head into the game in confident mood after hammering five goals past Burnley on Sunday.
O'Neill said: "Scoring five goals was very important for us.
"I don't care whether they are centre-forwards or wide men. Everyone likes to score to show people they have made a major contribution to the game.
"I think the players who scored will take great confidence from not only the goals they scored but the performance in the second half."
While Villa are battling it out against Palace, United will already have started their preparations for the final as they have an extra day to prepare.
O'Neill has taken that in his stride and he added: "It just falls that way. You cannot do anything about it.
"I remember when I was manager at Leicester City that we played an FA Cup fifth-round tie against Chelsea on the Sunday and then had to play Wimbledon in the semi-final of the League Cup the following Tuesday night.
"We asked for some help but it wasn't forthcoming. That's the way it goes."
O'Neill will not finalise his side until just before the match as Petrov is battling to shake off a virus.
Aston Villa v Crystal Palace. Click here to bet.