Ronaldo and Ibrahimovic are both in scintillating form ahead of the two-legged qualifying playoff but only one of their teams will end up in Brazil next year.
Both men scored hat-tricks at the weekend: Ronaldo in Real Madrid's 5-1 rout of Real Sociedad and the Swede netting all of Paris St Germain's goals in a 3-1 victory over Nice.
Portugal captain Ronaldo tops La Liga's best scorers' list with 16 goals while Ibrahimovic, with eight, is one behind Ligue 1 top marksmen Radamel Falcao and Edinson Cavani.
Ronaldo, 28, and Ibrahimovic, 32, are under pressure to deliver again on Friday, and in next Tuesday's return fixture in Stockholm, and Sweden coach Erik Hamren said his money was on his own man.
"I have Zlatan as number one, as he's my player," Hamren told reporters as the squad gathered in Stockholm ahead of the first leg.
"But Ronaldo is a very good footballer. You can keep an eye on him for 85 minutes and then he'll score two goals from nothing."
The same could be said of Hamren's captain Ibrahimovic, who picked up a seventh straight gold ball, the prize awarded to Sweden's best player, in the Swedish capital on Monday.
Portugal coach Paulo Bento said Sweden were difficult opponents.
"They are taller than us and physically strong, not just in set pieces but also through their direct football that feeds two tall, top-quality players," he said, referring to Ibrahimovic and Johan Elmander.
"It's up to us to make the match suit the characteristics of our players."
Bento also praised the resilience of the Scandinavians.
"Sweden were losing to Ireland, Germany and Austria and never gave up. They always keep their competitive edge going, no matter what".
The Swedes eventually lost to Germany in a 5-3 thriller despite a fightback but did manage 2-1 comeback wins in the Ireland and Austria qualifiers to finish second in Group C and earn a playoff spot.
Hamren has cast Group F runners-up Portugal as the favourites and expressed surprise that Bento had said the opposite.
"They are better ranked than we are. They were in a semi-final at the last Euros, so I don't know how he's thinking," Hamren said.
"According to me they are big favourites. They should be if you look at the ranking. They are favourites and we are the underdogs."
Goals will certainly be expected, not just because of the high-calibre hit men but also given that both camps have shown frailties at the back.
Of all World Cup qualifying runners-up, only Iceland (15) conceded more goals than Sweden (14) in the group phase.
Portugal allowed nine but question marks hover over goalkeeper Rui Patricio after a string of blunders.
Patricio, 25, gifted Israel a late 1-1 draw in October, misplacing a pass that landed right at an opponent's feet.
At the weekend, with Sporting, Patricio saw an awkward extra-time header comically slip between his legs as Benfica knocked Sporting out of the domestic Cup with a 4-3 win.
"He is the captain of Sporting and the number one of the national team; he has enough experience to deal with these moments," Portugal winger Nani said. "What is key is that he remains calm and has our trust."
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