Portugal were in danger of missing out on an automatic slot and needed an own goal from former Arsenal defender Johan Djourou to open the scoring.
Anything other than victory would have seen Portugal have to go through the play-offs, but when Andre Silva struck a second they were on course.
Switzerland started the night in pole position and were three points clear of Portugal but couldn’t get the job done.
Pop star Madonna was in the crowd to see Ronaldo and co progress.
They will now have to lock horns in the play-offs.
With Ronaldo’s team-mate Gareth Bale and Wales missing out, and Argentina in danger, it would have been a huge disappointment were Portugal, European champions last summer, to have missed out on Russia.
The Netherlands needed a huge seven goal swing against Sweden tonight to even get into the play-offs and have missed out altogether after only managing a 2-0 win.
European World Cup qualification
Who is through?
- France
- Portugal
- Germany
- Serbia
- Poland
- England
- Spain
- Belgium
- Iceland
Who is in the play-offs?
- Sweden
- Switzlerand
- Northern Ireland
- Republic of Ireland
- Denmark
- Italy
- Greece
- Croatia
Elsewhere Argentina must win in Ecuador to have any hope of making it.
Argentina, who reached the final three years ago in Brazil, lie in sixth place in the 10-team South American group, currently outside the qualifying places for Russia.
The top four qualify automatically and the fifth-placed side go into an intercontinental playoff against Oceania winners New Zealand.
“Argentina has shown the personality to demonstrate what it is, superior to the rest,” Jorge Sampaoli said in Ecuador on Monday.
“I hope we qualify because, looking beyond the numbers, Argentina deserves it.”
Argentina, who have won the World Cup twice, have taken just three points in their last four games. A win would guarantee Argentina at least fifth place but a draw might be enough to take them into the top four depending on results elsewhere.
Brazil have qualified already and Uruguay are almost certain to join them. Colombia, Peru, Paraguay, Argentina and Chile are all fighting for the remaining spots.
Sampaoli, who took over in June and has yet to record a competitive win, has not named his side for the match but Lionel Messi is sure to start.
“If we are up to Messi’s standards in tomorrow’s game then we’ll be alright,” Sampaoli said.
Argentina have beaten Ecuador only once in a World Cup qualifier in Quito, where the high altitude makes life difficult for visiting teams.