- Spain suffered a 2-1 home defeat by Switzerland as goals from Manuel Akanji and Breel Embolo knocked the hosts off the top of Nations League A-Group 2 on Saturday with one game left to play.
Last year's finalists are now second on eight points having been leapfrogged by Portugal, who breezed past Czech Republic 4-0 away to reach 10 points.
Cristiano Ronaldo's side will reach the final four with at least a home draw in Tuesday's crunch game against Spain, who must win in Braga to qualify for the semi-finals.
Switzerland are third on six points, two above than Czechs who they will face on Tuesday in a battle to avoid relegation.
Akanji opened the scoring with a header from a corner in the 21st minute, but Jordi Alba equalised for the hosts with a cross-shot from a counter-attack 10 minutes after the break.
Three minutes later, however, Embolo got the winner with a close-range strike from a corner.
(Reporting by Fernando Kallas; Editing by Ken Ferris)