NATAL, Brazil, June 17 (Reuters) - The United States are full of confidence after a dramatic win over Ghana but coach Juergen Klinsmann remains wary of a Portuguese backlash after the Cristiano Ronaldo-led side were mauled in their World Cup opener by Germany.
A last-gasp 2-1 victory over Ghana showed the United States could keep cool in a big match and they will need to do so again when they take on world player of the year Ronaldo on Sunday.
A win over Portugal in the Group G contest in the jungle city of Manaus should put the Americans through to the last 16 for the fourth time in the last seven tournaments.
But U.S. coach Juergen Klinsmann warned that Portugal's 4-0 thrashing by Germany could jolt them into action and the Americans have to cope with injuries to key players, including burly striker Jozy Altidore.
"Now they are going to come into Manaus pretty angry and I don't now how Ronaldo is going to perform when he is angry," Klinsmann told reporters. "We need to show Portugal how good we are."
Poor finishing, dreadful defending and indiscipline combined to make it a miserable opening game for Paulo Bento's side.
Five of Portugal's starting lineup against Germany were over 30, including three of the back four, so a more youthful U.S. team will aim to press the Portuguese in the hot and humid climate.
Portugal will also be without defender Pepe whose red card for leaning into Germany striker Thomas Mueller with his head rules him out.
The match will be the second World Cup meeting between the teams and the United States will hope for a similar result to 2002 in South Korea when they shocked a more fancied Portuguese side 3-2 in the group stage.
Although the United States are no longer surprise packages, they will be without striker Altidore whose hamstring injury against Ghana will probably rule him out of the rest of the tournament.
"It wasn't easy to swallow the first pill with Jozy coming off the field," Klinsmann said. "He is very, very important to us."
Klinsmann must also worry about his defence after Matt Besler failed to start the second half due to a tight hamstring. Replacement John Brooks ably filled in at centre back, marking his World Cup debut with a game-winning header.
More pressing is the health of Clint Dempsey who broke his nose after taking a boot to the face against Ghana shortly after scoring the fifth-fastest World Cup goal.
The captain said he had trouble breathing and coughed up blood during the match but Klinsmann predicted he would shake off the injury.
"You have got to deal with injuries," Klinsmann said. "It will happen more often in this World Cup. Players need to be ready." (Editing by Ed Osmond)