Now O'Neill has challenged his players to repeat that achievement in domestic football's number one cup competition.
Goals from Fabian Delph - his first for the club - Nathan Delfouneso and Ashley Young enabled Villa to overcome the League One side.
O'Neill said: "Can we reach two cup finals this season? We are certainly going to try. We've reached one already and now we're in the fifth round of the FA Cup.
"Of course, you need some luck with the draw and a lot of things can happen in cup matches which are one-off games.
"But if the quality players we've got here stay fit, there is no reason why we shouldn't try and achieve the double."
Delph has made only a handful of appearances since moving from Leeds in a £6million summer deal.
But he produced an impressive show against Gus Poyet's side and broke his scoring duck for the club during the second period.
O'Neill said: "Fabian was excellent in the last round against Blackburn and he again showed what a capable footballer he is. He has got a really good future ahead of him.
"He found it frustrating when he came here after playing over 100 successive games for Leeds.
"He started against Wigan on the opening day but I knew he would play a couple of games, then go out of the side, and then maybe play another couple as he got used to the Premier League.
"That can be frustrating and in addition a couple of our midfielders in James Milner and Stiliyan Petrov have been playing very well.
"It was tough for him to break through, but he will break through. He has a very good future in front of him."
Brighton boss Poyet, who played for Chelsea against Villa in the 2000 FA Cup final, took plenty of pride from his team's performance.
He said: "We put everything into the game and the fans were absolutely fantastic.
"We made a couple of mistakes and paid the price for that, but we showed during this game that we can compete with better players.
"I was never going to come to Villa Park and try and play for a 0-0 and be boring.
"That is not my style. I wanted to come and entertain and the boys can be proud of their efforts."