Saints beat Catalans Dragons 39-16 at home last week, but did not start the game well. Walmsley knows that Wigan will not let them get away with that again this week.
St Helens won 23-4 when the teams last clashed, in the last round of the regular season, at the DW Stadium in July.
“We have a cushion in the league now but that isn’t important,” Walmsley told his club’s official website.
“The league will take care of itself. We will take each game as it comes and what will happen will happen. We have to approach each game as do or die – that hasn’t changed.
“Wigan will be a different animal to the last time we faced them and will want to get one over us. We have to match that intensity because they will be coming at us.
“We were so far off the mark in the first half [against Catalans] and we cannot afford to do that again with the opposition we have to come up against in the rest of the Super 8s.”