Republic of Ireland captain Nathan Collins is still unable to provide an explanation for his side's 2-1 loss to Armenia last month before they welcome the same opposition to Dublin.

Irish World Cup qualifying hopes were dealt a seismic blow with the defeat in Yerevan last month against the group's lowest-ranked side.

The performance grew even more perplexing considering their brave showing at top seeds Portugal on Saturday night, albeit losing 1-0 to a 91st-minute Ruben Neves header.

The Brentford captain struggled to put his finger on what exactly went wrong in the embarrassing reverse against the Armenians when asked before Tuesday night's game.

"It's such an awkward one, football is such a mad sport, anything can happen, things change and it happens so quickly, momentum and how players feel," Collins said.

"We just never got going, I think [Armenia] grew in confidence from us struggling to get going, to create stuff. The togetherness we've seen in Portugal and the way we connected as an 11, was completely different to how we connected together in Armenia.

"I think Armenia took confidence from that, they took that confidence away from us. They probably had better chances, better spells, and they looked a better team.

"We have belief that we are a better team than that. We have belief that we can go and beat big teams and go against these teams and we can get results and put in good performances like Portugal. Sometimes there's no clear explanation why, but it's tough to take."

The Republic of Ireland are still searching for their first win of this World Cup qualifying campaign, and occupy bottom spot in Group F, with just one point from their first three games, but victory on Tuesday could potentially lift Heimir Hallgrimsson's side up to second and into a play-off spot.

Saturday's performance in Lisbon appears to have restored pride back in the green jersey, and much-needed confidence back into the players, after the criticism they received in the aftermath of the defeat by Armenia.

"Listen, playing for Republic of Ireland is one of the biggest honours and it's not easy at all because every kid growing up wants to play for Republic of Ireland," Collins continued.

"It's a different game, but the pressure to play for Republic of Ireland is a privilege, the pressure of putting that green jersey on is something you always wanted and it's something I'll never take for granted.

"I think for the message we wanted and what we put out [in Portugal], I think it all came together really nicely and I think it can help us in confidence.

"But again, it's going to be a different game, and we still have to have that inner belief that we can go and dominate, hurt and score goals against Armenia."