Portugal coach Fernando Santos said: "We had our chances and deserved to win." In the other Group B match on Friday, Luxembourg defeated Lithuania 2-1. Ronaldo hadn't played for Portugal since its elimination by Uruguay in the round of 16 at the World Cup in Russia.
Portugal has qualified for the semifinals of the inaugural Nations League, along with Switzerland, the Netherlands and England, and will host the finals in June. The home team's first real chance on Friday came when William Carvalho's goal was disallowed for offside.
Ronaldo's first opportunity was in the 22nd minute with a low shot from inside the area saved by Pyatov. The goalkeeper denied him again five minutes later, diving to his right to deflect his low shot following a run inside the area.
Pyatov also made a difficult stop from a curling shot by forward Andre Silva early in the second half, and also thwarted defender Pepe. Ukraine, which next season will play in the top tier of the Nations League, did not get past the group stage of Euro 2016 in France.
Ukraine visits Luxembourg on Monday, while Portugal hosts Serbia.
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