Cristiano Ronaldo came off the bench to score the winner as Portugal earned a 2-1 victory, condemning Scotland to another late defeat.
The 39-year-old, who started on the bench in a competitive match for the first time since the 2022 World Cup, added to Bruno Fernandes' strike after Scott McTominay had given Scotland the lead early on.
The home crowd were just as stunned as Portugal's defence when McTominay snuck in behind, thumping Kenny McLean's cross past a stranded Diogo Costa after just seven minutes.
The hosts certainly had their chances to get back into the game though – Angus Gunn made a brilliant save to deny Rafael Leao, who also fired a number of efforts wide of the left post.
Though Scotland tried to continue soaking up the pressure, their defence was eventually breached nine minutes after the break, with Fernandes marking his 30th birthday with a sweeping finish from 20 yards out.
Gunn smothered Joao Felix's low shot in the 78th minute before Ronaldo came within millimetres of a winner as his header hit the inside of the far post.
But Ronaldo would have the final say as he stretched out a leg in the six-yard box to turn Nuno Mendes' cross into the back of the net.
Steve Clarke could not have asked for more from his team in the first half, as they scored with their only effort, but also resolutely defended as Portugal racked up 16 shots (three on target), creating 1.21 expected goals (xG).
It was a regular creator that got the Selecao back on level terms though, as Fernandes got his 21st goal involvement under Roberto Martinez in all competitions, at least five more than any other Portugal player (11 goals, 10 assists).
And Ronaldo is now up to 901 career goals, with only Aleksandar Mitrovic (14), Erling Haaland (12) and Romelu Lukaku (10) bettering his nine-goal tally in the Nations League.