In one of just two all-European ties amid a diverse last 16, two teams who experienced very different fortunes in their final group fixtures contest a precious place in the quarter-finals.
A successful start to their Qatar 2022 campaign left Portugal needing just a point in the final round of group matches to be certain of finishing first, and qualification for the knockout stages had already been assured.
When Ricardo Horta - one of a number of fresh faces introduced for the occasion by coach Fernando Santos - put them ahead against South Korea in the fifth minute, it seemed the Selecao would stroll straight through. Yet, their opponents staged one of several comebacks that have characterised the finals' first fortnight: equalising before the break and then producing a dramatic 91st-minute strike to condemn them to a 2-1 defeat.
Despite suffering their first setback, Uruguay's victory over Ghana sealed Portugal's progress as Group H top dogs, and they now seek to successfully negotiate the last 16 for the first time since 2006, when they ultimately finished fourth in Germany.
Having seen his side start their World Cup by beating Ghana 3-2 and then adding a 2-0 win against Uruguay last Monday, when Bruno Fernandes found the net twice, Euro 2016 winner Santos can feasibly aim to break new ground this winter.
A Eusebio-inspired Portugal finished third at the 1966 World Cup, but for all their success at youth level the Iberian nation has never made it to a senior global final. Indeed, two of their last three campaigns ended in the first knockout round.
With speculation still raging about the form and fitness of one-man record machine Cristiano Ronaldo, Santos must get his team selection spot on in Lusail, as the Selecao encounter familiar opposition with a proven track-record in major finals.
When they last met their Swiss counterparts in the UEFA Nations League earlier this year, there were two very different outcomes in the space of a few days: Portugal were comprehensive 4-0 winners in Lisbon - with Ronaldo bagging a first-half brace - before Switzerland then turned the tables with a 1-0 victory in Geneva.
After that summertime win in the Nations League, Switzerland went on to beat both Spain and the Czech Republic in the same competition, before kicking off their improbable quest for a first World Cup by winning two of their first three games in Qatar.
A point was thought to be enough for the second-placed Nati to qualify from Group G, after their 1-0 defeat of Cameroon was followed by a loss to Brazil by the same scoreline, but Cameroon's incredible success against the Brazilians completely changed the picture.
It therefore took a hard-fought 3-2 victory over Serbia in the sides' fiery encounter at Stadium 974 - during which 11 players were booked by the referee - to seal progress to the last 16.
Goals from Breel Embolo, Remo Freuler and opening scorer Xherdan Shaqiri - who celebrated by shushing the Serbian fans who jeered his every touch - saw them through, as Granit Xhaka narrowly escaped receiving a red card at the end of a tempestuous encounter.
The Swiss have never before won three matches at a single World Cup finals, and have failed to reach the quarter-finals in their past seven attempts, but just 90 minutes - plus perhaps a little more - now separates Murat Yakin's side from such a feat this year.
Not since they hosted the World Cup in 1954 have Switzerland reached the last eight, but having seen off neighbours and reigning world champions France to make the quarters at last year's Euros, a squad well versed in the ebbs and flows of knockout football will surely fancy their chances on Tuesday.
With progress assured from Group H, Fernando Santos used the opportunity to make six changes to his Portugal XI last time out, but the notoriously conservative coach should revert to type on Tuesday night.
Captain Cristiano Ronaldo was one of three players replaced after 65 minutes on Friday, though, and the Selecao's record goalscorer now finds himself consigned to the bench, with Goncalo Ramos starting up front instead.
Only given his first Benfica start in August, 19-year-old defender Antonio Silva was handed a competitive debut against South Korea alongside veteran campaigner Pepe - a man 20 years his senior. The youngest Portuguese player to feature at the World Cup makes way, however, as Ruben Dias returns to the back four; Diogo Dalot made a big impression on his first World Cup start and is retained.
Switzerland will be hoping stalwart goalkeeper Yann Sommer can return to bolster their back line at Lusail Stadium, after missing their final Group G match due to illness. With 30 clean sheets and innumerable crucial saves across his 76 caps for the Nati, Sommer would come back in for Borussia Dortmund's Gregor Kobel if available.
There is every chance that Murat Yakin's side will be otherwise unchanged, as Granit Xhaka and Remo Freuler provide the midfield screen ahead of a well-drilled defence and Breel Embolo leads the line up front.
Portugal possible starting lineup:
Costa; Dalot, Pepe, Dias, Gurreiro; B. Silva, Carvalho, Otavio; Fernandes; Felix, Ramos
Switzerland possible starting lineup:
Sommer; Fernandes, Akanji, Schar, Rodriguez; Freuler, Xhaka; Shaqiri, Sow, Vargas; Embolo
We say: Portugal 2-1 Switzerland (after extra time)
Given such an abundance of attacking talent, Portugal rarely have a problem with scoring - but protecting a lead is often another matter.
The persistent negativity of Fernando Santos often sees the Selecao retreat, which would allow a capable Swiss side to come into their own and force extra time. Nonetheless, the big-game nous of Pepe, Ronaldo and co should just see them over the line.
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