Almost four million people watched Portugal's clash with Ghana at the 2022 World Cup in Qatar, which was broadcast on TVI.
It is the most-watched game in Portugal so far, according to figures presented by Universal McCann (UM).
On Thursday, Portugal beat Ghana 3-2, in Doha, in the first game at the 2022 World Cup.
Ronaldo became the first player to score in five World Cups after converting a opener from the spot after he was fouled by Mohammed Salisu.
Ghana equalised against the run of play when Andre Ayew, their own veteran striker, fired home from close range, but Portugal immediately responded with quickfire goals from Joao Felix and substitute Rafael Leao before a late Ghana consolation by Osman Bukari.
"TVI broadcast the debut game which had a total of 3.9 million people watching, with an average audience of 2.3 million and a share of 64.5 percent", says UM, the media agency of the Mediabrands group.
Both teams are back in action on Monday. Portugal take on Uruguay and Ghana play South Korea.