The match in Leiria proved an uncomfortable watch for Portugal supporters. Ronaldo was chosen to lead the line from the start but failed to convert opportunities that, at his peak, would have been routine.
In the ninth minute, he ran onto a through ball from Nelson Semedo with only the goalkeeper to beat and fired wide. Moments later he miskicked a further effort. When the ball came back off the advertising hoardings into his path, Ronaldo blasted it away in visible frustration.
Portugal eventually broke the deadlock in the 23rd minute through winger Pedro Neto, who finished calmly to give the hosts the lead. Nigeria, who did not qualify for the World Cup, drew level before half-time through Akor Adams.
At the break, Roberto Martínez made nine substitutions — removing all outfield starters except Ronaldo, who continued into the second half alone from the original eleven.
A further chance came and went early in the second period when Ronaldo ballooned a left-footed effort from a low cross near the penalty spot. He was finally withdrawn in the 65th minute, replaced by Gonçalo Ramos.
Francisco Conceição — one of the second-half substitutes — scored the winner in the 75th minute to seal a 2-1 victory.
Martínez was asked after the match why Ronaldo had been kept on for the start of the second half despite the wholesale changes around him.
"The plan we had for Cristiano, based on the information available to us, was for him to play either 45 or 60 minutes. The important thing is to work on the individual aspect, but also to have a team capable of finishing the match stronger than it started. That reflects good work, focus, and clarity in the way the ideas are being executed. We are now much better prepared."
The manager's praise for the collective masked the individual story. Ronaldo's goalless display — his first appearance of the summer — will intensify questions over whether the five-time Ballon d'Or winner should start Portugal's opening World Cup fixture.
He turned 41 in February and has spoken publicly about wanting to reach the World Cup as a meaningful contributor rather than a ceremonial presence. His form at Al-Nassr in the Saudi Pro League remained productive — he scored 33 goals across all competitions last season.
Whether those numbers translate onto the biggest stage, against the best defences in the world, is the question every neutral and every Portuguese supporter will be asking as the tournament opens.