"I believe in the manager, I believe in the players, I believe in all the backroom staff".
The two sides will now reconvene at the Aviva Stadium in Dublin on Tuesday where Denmark will know that a score draw in 90 minutes will see them through to Russian Federation on the away goals rule. Denmark's home advantage between the two legs of the play-offs has been wiped out, but Ireland have plenty of work ahead of them still for two reasons.
After describing the game as "a physical battle", O'Neill said: "The players put a big effort into the game". But I think we are capable of doing that.
"They are a very good team, very good players, but they don't have the character and the heart and the desire that we have".
"We'll be hard to beat, disciplined", Duffy said.
The Danes will arrive in Dublin on Tuesday evening having been booed off by sections of the home crowd at the Parken Stadium on Saturday night after the Republic frustrated them for 90 minutes to snatch a 0-0 draw in the first leg of their winner-takes-all play-off. It's about keeping the tempo for us and taking the chances we do get. "I'm really confident. We know it will be a tough game".
David Meyler may be a contender to start in the second leg after his magnificent performance in Wales and the team may need to be freshened up after what would have been a draining night both physically and mentally with all the pressure that was on that game.
MARTIN O'NEILL ACKNOWLEDGED that his Ireland side will need to be better in possession if they're to qualify for the 2018 World Cup at Denmark's expense.
We may have missed an opportunity to get even more out of the away leg, but let's believe that we will all be celebrating when it matters most.
He added: "We would obviously want to be better with the ball in Dublin when we are playing in front of our home fans, and in all honesty, we will need to be if we have to score a goal".
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