Following Saturday's 1-1 draw in Georgia, in which the Brighton defender opened the scoring, Ireland sit in second place in Group D, two points behind leaders Serbia and two ahead of third placed Wales.
This means that the match against the group leaders on Tuesday is vital to the Republic's hopes of qualifying for the World Cup in the summer but Duffy was upbeat following the draw in Tbilisi.
"We know it's a huge game and if we win that then we can potentially top the group. If we do that, we're one step closer to the World Cup," Duffy said.
"They [Georgia] dominated and we knew they could take points off teams because they're a good team. That little final bit of end-product is probably what they don't have and bigger countries do.
"For me personally, I'd say they're better than some of the teams ranked above them. On paper, it's not a glamorous team but that was difficult, and at home it was too.
"We want to beat those teams, but if you can't beat them, you need to avoid defeat and we did that. We'll take that positive on to Tuesday."
Duffy's compatriot Harry Arter added: "We want to beat those teams, but if you can't beat them, you need to avoid defeat and we did that. We'll take that positive on to Tuesday."