Giovanni Trapattoni's men head for the Friends Arena in Stockholm on Friday knowing victory would put them in the driving seat to claim second place in Group C behind favourites Germany. By the same token, defeat four days before they entertain their other main rivals, Austria, at the Aviva Stadium would represent a massive blow to their own hopes.
Sweden famously pulled off a stunning fightback in Germany when, after trailing 4-0, they fought back to snatch a 4-4 draw, and Clark said: "The game is 90 minutes-plus, so you can't take your foot off the gas no matter what is happening."
He added: "They can score goals, they have shown that, and it's about us trying to prevent that and for us going out there to get the win. But it's a game of 90 minutes and you can't take your foot off the gas at all.
"The lads here have been brilliant the last two days in training, and we will work hard now leading up to the game and work hard on ways we can win the game.
"All the lads are confident we can go and get something out of the game."
Paris St Germain striker Zlatan Ibrahimovic launched the spectacular comeback in Berlin with his side's first goal, and his presence in the starting line-up could present the Republic with real problems if he performs to his best.
Clark will hope he gets a chance to test himself against the hugely-destructive frontman, whose methods will be drummed into the Aston Villa player and his defensive colleagues in Malahide over the next couple of days.
Asked how Ibrahimovic can be stopped, Clark said with a smile: "I don't know, to be honest. We are going to work on it in the next few days in training and hopefully we can do enough to do it.
"It's a team of 11 players, it's not just a one-man team. They have got some top-class players, they are all going to be well up for the game and we need to keep an eye on everyone, not just one man."
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