If they continue performing as they have in victories over Turkey and the Czechs, anything is possible.
"If we're carrying on playing like this as a unit, we've got great chances," star winger Cristiano Ronaldo said.
Ronaldo's first goal for Portugal since October was the winner. It came in the 63rd minute off a brilliant pass by playmaker Deco, who scored Portugal's first goal. Substitute Ricardo Quaresma clinched it in injury time off a pass from Ronaldo.
That gave the Portuguese six points, with a game against co-host Switzerland to come, and the Group A title.
Led by their Brazilian coach Luiz Felipe Scolari, Portugal is trying to reach its second consecutive final at Euros. It was runner-up to Greece four years ago at home. It had another successful campaign at the World Cup in Germany two years later, losing to France in the semifinals.
Scolari was unhappy with the first half, which ended 1-1.
"I said they had to be more aggressive," Scolari said. "We had to show the opponent we know how to impose ourselves."
On Portugal's first goal, Ronaldo tried to exchange passes with Nuno Gomes. Goalkeeper Petr Cech intercepted the return with his leg and redirected it into Deco's path, leaving the diminutive midfielder to force the ball into the net from close range, the ball deflecting off defender Marek Jankulovski.
Portugal controlled possession, but often had trouble penetrating the Czechs.But midfielder Sionko equalized nine minutes after Decos scored with a strong header from in front of goal, beating Portugal's Armando Petit to the ball off a corner by Jaroslav Plasil.
The Czechs, who have three points and next play Turkey, got a goal on a header by Libor Sionko off a corner kick in the 17th . They beat Switzerland in their opener.
"We failed to score more goals and that decided the match," Czech midfielder Marek Matejovsky said. "I'm 100 percent sure we'll advance."
Scolari was impressed with the work of Deco.
"Deco has been having some great games with the national team and also is in an excellent moment physically," Scolari said. "This is the Deco that I want. Nobody tries as hard as Deco. He makes mistakes because he tries more. I hope he keeps making the mistakes he did today, because then he will keep doing what he did today."