Switzerland had lost all three of its Group A2 fixtures, including a 4-0 hammering in the reverse fixture, but took the lead through Seferovic inside the first minute.

Fernando Santos's side was repeatedly denied by Swiss goalkeeper Jonas Omlin in search of an equaliser, with the absence of the injured talisman Cristiano Ronaldo particularly noticeable for the visitor.

Defeat left Portugal a point behind Spain at the summit of the group, while Switzerland picked up its first win to move one point behind Czech Republic in third.

Switzerland raced out the blocks as Seferovic headed into the bottom-left corner from Silvan Widmer's right-wing cross after just 55 seconds – the fastest goal in Nations League history.

The host thought it had a penalty 13 minutes later for a Nuno Mendes handball, but a lengthy VAR check ruled the spot-kick out for an earlier Nico Elvedi foul on Andre Silva.

Omlin kept his side ahead by denying a close-range Danilo Pereira header, before Rafael Leao headed home shortly after, only to be ruled out for offside.

Omlin also stopped a low Andre Silva drive after the interval, while Remo Freuler drilled just wide at the other end.

Seferovic almost extended Switzerland's lead but arrowed narrowly off target on a rapid counter-attack before Omlin beat away a swerving Bernardo Silva long-range strike.

The Montpellier stopper carried on his fantastic performance by pushing away a sliding Goncalo Guedes effort and a low Diogo Jota header as Switzerland held on for victory.