Ireland thumped South Africa 32-15 last Saturday to lunch their autumn in stunning fashion but Australia, who are close to full strength, will be a far tougher assignment.
The home side are praying for good conditions so their explosive backs can cut loose once again in what should be an intriguing showdown between two classy three-quarter lines.
And Horgan, who was in magnificent form against the Springboks, believes Ireland's wish that Lansdowne Road remains dry on Sunday underlines just how far the national side has come.
"We scored four tries against South Africa and could have finished with a couple more. That's a new experience for us against southern hemisphere opposition," he said.
"The last time we beat Australia was in 2002 when it was a filthy day. It shows the evolution of Irish rugby that back then we were looking for a bad day so we could kick to the corners.
"That attitude doesn't exist anymore. We want a dry day where we can keep the ball in hand, attack teams and implement our gameplan. We're not waiting for the opposition to have a bad day.
"We want to impose ourselves and we know that if we have a good day, it will be very difficult for anyone to live with us.
"We're the most confident I've seen since I've been involved in the Ireland team. The confidence has built up over a long time, although there was a blip around this time last year.
"When I first started we just didn't beat southern hemisphere teams, it didn't happen. We weren't used to beating France or England, never mind the southern hemisphere.
"But now you look right down the ranks of Irish rugby and the situation is changing. We're beating the big names in rugby and that breeds confidence across all levels."
Gordon D'Arcy was named man of the match against South Africa but Horgan could easily have taken the honour with a destructive display which saw him pierce the Springbok defence time and again.
The 28-year-old threatened out wide, finishing one try and setting up another, but was at his most dangerous when coming in off the wing and marauding through the midfield.
Having played both positions during his international career, Horgan's initial preference for the centre has since been replaced by the attraction of a roaming role on the wing.
"It's important for me to get my hands on the ball. I played a lot of my early rugby in the centre and that has left me wanting to be involved as much as I can," he added.
"For a modern day rugby player the positions are very interchangeable. We have guys in the team who can play at first or second receiver, or do a job out wide and have the ability to play at full-back.
"Australia have guys who can play all positions in the backline. Matt Giteau is a prime example of that as he has been swapped from centre to scrum-half.
"But my preference is now for the wing. I've realised you don't have to stand out on the wing and wait for the ball to arrive.
"Wing gives me a lot of freedom in that respect. It allows me to experiment whereas playing in the centre is more rigid. The wing suits me better now."
Horgan will be winning his 50th cap on Sunday, finally allowing him to join a special group within the squad.
"Five of us won our first cap on the same day, Ronan O'Gara, Peter Stringer, John Hayes, Simon Easterby and me," he explained.
"I'm the last one of that particular vintage to reach the 50-cap milestone and I'm delighted to get there. It's nice to be part of the club."