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The 32-year-old Real Madrid star's early header secured a 1-0 win at Moscow's Spartak Stadium and left Fernando Santos' men a point clear of the Russians at the top of Group A.
Only goalkeeper Igor Akinfeev, who was winning his 100th cap, denied Portugal victory by a greater margin as he made vital saves from Ronaldo and Andre Silva either side of half-time.
Russia were poor before half-time and although they improved after it, they were repeatedly hit on the break as they committed men to the search for an equaliser.
Ronaldo, making his 141st appearance for his country, needed just eight minutes to make his mark, although the opening goal was far from all his own work.
With the Russians attempting to sit in and deny Portugal space in the middle of the field, Raphael Guerreiro was given just that wide on the left to deliver an inviting cross to the far post, where the Real Madrid striker made the most of defender Fedor Kudriashov's misjudgement to head home.
Ronaldo proved the main threat throughout the first half as the hosts offered little going forward, and he tested Akinfeev with a 25th-minute free-kick before forcing the keeper to block with his legs seven minutes later.
Russia might have been level as the half-time whistle approached, but striker Fedor Smolov could not adjust his feet in time to steer Aleksandr Golovin's cross on target.
Skipper Akinfeev kept his side in it when he clawed away Silva's 50th-minute header from close range, and he was in the right place at the right time to repel Cedric Soares long-range effort nine minutes later.
The Russians, who beat New Zealand 2-0 in their opening fixture, belatedly launched their push and might have been level just after the hour when Alexander Samedov's teasing cross was only fractionally too high for Smolov in the middle.
But Ronaldo passed up a glorious opportunity to extend his side's lead just past the hour when he headed wide from Andre Gomes' cross as Portugal broke at pace.
However, it was Russia who finished strongly with substitute Aleksandr Bukharov appealing in vain for a last-gasp penalty after going down in the box before defender Georgy Dzhikya heading inches over Rui Patricio's crossbar deep into injury-time.
