A landmark goal from Cristiano Ronaldo helped the Selecao start with maximum points in League A Group 1, while Scotland sunk to another last-gasp defeat.
Match preview
An early strike from former clubmate Diogo Dalot set the stage for Cristiano Ronaldo to score his 900th career goal on Thursday, as Portugal secured a 2-1 win in their Nations League opener against Croatia.
Dalot had fired home after receiving a through ball from Manchester United colleague Bruno Fernandes, before Ronaldo's finish put the hosts in control of proceedings in Lisbon, albeit a Dalot own-goal later reduced their advantage.
Having been eliminated in the quarter-finals of Euro 2024, the Selecao produced a positive response upon returning to action, with their all-time appearance holder and record scorer quietening claims he should step away from the national team.
Head coach Roberto Martinez will ultimately be aiming to go all the way in a tournament Portugal won in 2019: they missed out on a place in the finals by finishing second to Spain in their group last time around.
Now, the ex-Belgium boss targets maximum points from a home double-header, though even finishing second in Group 1 would be enough to reach the quarter-finals in UEFA's new extended format.
Aside from two goalless draws, Scotland have been beaten in each of their previous meetings with Portugal, so history will not be on their side at Estadio da Luz.
Much has changed since their last encounter in 2018, as Steve Clarke's reign has seen the Scots return to somewhere near their former status, reaching successive European Championship finals and earning promotion to the top tier of the Nations League.
However, a truly miserable run of results continued earlier this week, as Poland converted a stoppage-time penalty to win 3-2 at Hampden Park, following a valiant Scottish fightback.
New Napoli signings Billy Gilmour and Scott McTominay both scored second-half goals to pull the hosts level in Glasgow, but Grant Hanley's tired challenge felled Nicola Zalewski late on, and the winger then stepped up to beat Angus Gunn from the spot.
Scotland have now conceded 17 goals in eight matches this year, including one in another late heartbreak against Hungary as they exited Euro 2024 with only one point from three games.
Just one win from 13 throughout 2024 puts pressure on Clarke to avoid another defeat this weekend - particularly as finishing third or fourth could see Scotland relegated - but the calibre of their opponents makes that a tough task.
Portugal Nations League form:
W
Portugal form (all competitions):
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W
L
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L
W
Scotland Nations League form:
L
Scotland form (all competitions):
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D
L
D
L
L
Team News
Rarely predictable in terms of tactics or personnel, Portugal coach Roberto Martinez switched from a back four to a three midway through Thursday's game against Croatia, so either setup could be used this weekend.
Pedro Goncalves and Francisco Trincao were both recalled to the squad this month, and they will compete with Rafael Leao and Pedro Neto for selection in support of captain Cristiano Ronaldo, who is set to start up front.
After Nelson Semedo and Joao Neves were introduced at half time, either - or both - could be promoted to the starting XI if Martinez decides to rotate his abundant resources.
Meanwhile, Steve Clarke - now without Celtic captain Callum McGregor after his international retirement - sent on Ryan Gauld and Ben Doak for their senior debuts last time out, but it should be a familiar Scotland side that lines up in Lisbon.
Joining first-choice defender Kieran Tierney on the sidelines, Torino striker Che Adams had to withdraw due to injury, so either either Lawrence Shankland or Lyndon Dykes will lead the line on Sunday night.
The visitors' main threat could come from just behind the frontman, though, as Scott McTominay moved onto 10 international goals with his midweek strike against Poland.
Portugal possible starting lineup:
Costa; Dalot, Dias, A. Silva, Mendes; Neves, Vitinha; B. Silva, Fernandes, Leao; Ronaldo
Scotland possible starting lineup:
Gunn; Ralston, Hanley, McKenna, Robertson; McClean, Gilmour; McGinn, McTominay, Christie; Dykes