Portugal boss Fernando Santos said the country's Euro 2016 triumph "must be forgotten" after his side lost in the opening qualifier for the 2018 World Cup.
Switzerland controlled the European champions on Tuesday in a 2-0 win with goals from Breel Embolo and Admir Mehmedi.
The defeat was Portugal's first in a competitive fixture since Santos took over two years ago, and he urged his team to look forward.
"We started the game well, we dominated the first 15, 20 minutes but then we were dazzled and were a bit pragmatic," Santos told RTP.
"We conceded in the only time that Switzerland was near our goal and afterwards we stepped back and allowed them to win individual battles -- the European championship has to be forgotten.
"We were not as strong as we usually are. We are in qualifying and that cannot happen."
Portugal were without the injured Cristiano Ronaldo, so when they needed a goal Santos brought on Andre Silva and Joao Mario, while Nani moved into a central role and hit the post in the late stages of the game.
"Trailing 2-0, I tried to change things, play with two strikers. We had chances to score, we could have created more," Santos said.
"In the latter stages, Switzerland just defended but we created some danger in the final minutes when we played with more heart.
"If we had scored a goal, we could have got back in the game."