Cristiano Ronaldo scored as Portugal beat Poland 3-1 for their third straight Nations League win on Saturday, while European champions Spain put an end to Denmark's perfect start in the competition.

Bernardo Silva volleyed Portugal ahead in the 26th minute in Warsaw as Bruno Fernandes cleverly nodded a cross from Ruben Neves back towards the Manchester City midfielder.

Ronaldo then found himself in the right place at the right time to turn in the rebound for Portugal's second after Rafael Leao's shot came back off the post following a brilliant surging run by the AC Milan winger.

The 39-year-old Ronaldo has now struck in all three games of this Nations League campaign for Portugal, taking his record men's international goals tally to 133.

Piotr Zielinski cut the deficit for Poland but Jan Bednarek's own goal sealed victory for Portugal, the lone remaining team in League A with a 100 percent record, and they could secure a place in the quarter-finals next week.

"We worked very hard the last few days, preparing various solutions for this game, and we were able to show it on the pitch. I am really satisfied because we controlled this game," said Portugal coach Roberto Martinez.

"We played great as a team."

Portugal have a maximum nine points in Group A1, three ahead of Croatia who beat Scotland 2-1 to condemn their opponents to a third successive defeat in the section.

Ryan Christie's first half-goal gave Scotland a shock lead in Zagreb, but Igor Matanovic equalised before the interval and Andrej Kramaric bagged the winner midway through the second half.

Che Adams thought he had salvaged a stoppage-time equaliser but VAR disallowed his effort for offside, with Scotland winless in nine competitive outings -- the longest run in their history.