The Portuguese ran riot against the Swiss when they met in the Nations League in Lisbon, but they lost 1-0 in the return fixture a week later.
"I'm sure we'll face a Swiss team with a lot of possession and we are ready for that, There have been surprises (at this World Cup), that's a fact, we need to be focused from the first minute to the last so that things go our way, and not the other way," Carvalho told reporters on Sunday.
The Portuguese were on the wrong end of one of those shocks, losing 2-1 to South Korea before bouncing back with wins over Ghana and Uruguay that put them through as Group H winners.
A European champion with Portugal in 2016, Carvalho spoke to reporters, keeping his answers short ahead of his side's training session as the sun went down.
"I think Portugal needs to play like we did in the first two games - united, from start to finish. We know that we will be up against a very tough opponent, and the details will make all the difference, we need to be ready," he said.
"We're talking about two big national teams, both will do their utmost to win, and details will make the difference," he repeated.
"In both teams we have top players, and from day one we knew we want to get as far as possible, but right now we have to focus on the Swiss," he added.
