"The players are feeling we can bring the confidence from the other evening into the game and we believe we can win tomorrow," O'Neill said at a news conference.
"We want to go out blazing tomorrow. We want to stay in Euro 2016 and we feel we can do it.
"The goal against Italy epitomises the spirit we have in the team. The players have embraced the tournament.
"We know we face a team full of quality players, especially in midfield. But we are full of confidence heading into the game."
Penalties could decide Sunday's match if both sides remain on level terms after 120 minutes and O'Neill has stressed Ireland have done everything within their powers to prepare for such a scenario.
"We have practiced penalties throughout the time we've been in camp," he added.
"We've done as much as we can on that aspect."