Vern Cotter's men face the unbeaten Wallabies at Twickenham having finished second in Pool B behind South Africa.
Australia are heavy favourites to progress to the last four having seen off Wales and hosts England in the pool stage.
Seymour said: "Entering the quarter-finals it is one game and if you don't get that one game right, it is the end of the finals, and we are playing a team that have played some of the best rugby in the competition so far.
"All the guys in the squad have ample of experience of high-pressure situations.
"This is the quarter-final of the World Cup and there is still a lot of differences with other environments, but we are all professional players and are all settled on what we need to do."
Australia's pack have excelled so far in the competition and enjoy one of the highest scrum success percentages, but prop Gordon Reid is hopeful Scotland's forwards can match the Wallabies.
"They are a tight group of players," Reid added. "We watched them against Wales and England and we have to keep on doing what we have to do.
"Our scrum was pretty poor in the Six Nations, but we've improved hugely over the last year after changing our whole set up in the scrum.
"We've got a bit of belief. Our first objective was to get through and it is now knock-out rugby and anything can happen."