Portugal will host Sweden in Lisbon on Friday before both teams head to Stockholm for the second leg on Tuesday to decide who will qualify for Brazil 2014.
While Hamren maintained he has 'a good feeling' about his team, he had no hesitation installing Portugal as favourites for the first leg.
"Portugal are favourites for three reasons," Hamren said on Thursday.
"They are better ranked than us.
"They showed at the 2012 European Championships, they nearly got to the final. They lost on penalties to Spain.
"Also, they are playing at home here.
"They are big favourites but we believe in ourselves and remember that it's two games and four (halves of) 45 minutes. That's the challenge and that's the thing we're working hard for."
The two-legged playoff has been billed as a head-to-head battle between each team's star striker; Sweden's Zlatan Ibrahimovic and Cristiano Ronaldo of Portugal.
Hamren insisted, however, that Ibrahimovic and Ronaldo could cancel each other out, meaning the tie will be decided by the other 20 players on the field.
"We need the team to be good, if we are to use Zlatan we need to be good as a team because he needs that support," the 56-year-old coach said.
"If we are playing good, if we are strong as a team, then he can be the match winner."
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