Portugal have muddled through their opening two matches in Russia thanks to the brilliance of Cristiano Ronaldo, whose four goals have helped them collect four points, after a 3-3 draw against Iberian rivals Spain and an edgy 1-0 win over Morocco.
Against Spain, Portugal had only 39 percent possession, yet managed a draw thanks to Ronaldo's hat-trick, while against Morocco, they struck early and then clung on for dear life at the end.
That has left them needing one point on Monday against Iran, a team led by former Portugal coach Carlos Queiroz, to secure their spot in the last 16.
Dias said there were some nerves ahead of their final group match, with the team having failed to hit top gear as yet in Russia.
"Anxiety exists because it's a World Cup and we are European champions and we want to get through the group and go as far as possible," Dias told a news conference at the Portugal training base.
"But it's all relative. We have really good players and we all have the same objective. Sometimes things don't work out the way you want... but it's a World Cup."
Portugal's cagey performances bear a striking similarity to Euro 2016, when they triumphed after scraping through the group stage without winning a match and then won every single knockout game having less possession than their opponents.
Dias, however, said they were warming to the task and performances should improve as the tournament in Russia wears on.
"Sometimes, things aren't so good at the start and you start improving during the competition and gaining in confidence," the Benfica defender said. "This is natural...You start gaining confidence naturally."
(Writing by Toby Davis; Editing by Ian Chadband)
