Ronaldo, 39, put behind him a disappointing Euro 2024 in which he failed to score as he turned in a Nuno Mendes cross in the 34th minute at the Estadio da Luz to reach the landmark.
He appeared emotional as he celebrated the goal, his 131st in a Portugal shirt. Half of his goals were scored for Real Madrid, with the remainder spread across his spells at Sporting Lisbon, Manchester United, and his current club Al-Nassr.
Diogo Dalot’s goal had put Portugal in front early on before Ronaldo netted, with a Dalot own-goal reducing the deficit before the break.
The teams are in Group A1 of the latest edition of the Nations League along with Poland and Scotland.
Portugal next host Scotland, who lost 3-2 to Poland, in Lisbon on Sunday.
Poland had been 2-0 up as Sebastian Szymanski gave them an early lead and captain Robert Lewandowski added a penalty just before the break.
However, Billy Gilmour pulled one back for League A newcomers Scotland moments after the restart, and Scott McTominay equalized before Roma’s Zalewski sneaked his spot-kick under Angus Gunn deep into stoppage time.
Elsewhere, there were wins for Slovakia and Northern Ireland in League C, while Sweden now being coached by Jon Dahl Tomasson beat Azerbaijan 3-1 away in Baku with Newcastle United’s Alexander Isak netting twice.
History was made in League D as San Marino, the world’s worst team according to the FIFA rankings, beat Liechtenstein 1-0 to claim their first-ever competitive win.