Ronaldo, who scored a hat-trick in Real's 6-1 opening day victory over Galatasaray, and Angel Di Maria both struck twice as the Spaniards swept the visitors aside at the Santiago Bernabeu.
The Portugal international marked his 100th appearance in European club football with a 21st-minute header, and then doubled his tally 20 minutes into the second half before Di Maria sealed the win with two goals inside the final 19 minutes.
Real stand four points clear of second-placed Juventus, who were denied victory in a dramatic conclusion to their 2-2 home draw with Galatasaray.
Didier Drogba's first-half strike had given the Turkish outfit the lead, but Arturo Vidal levelled with a 76th-minute penalty and substitute Fabio Quagliarella thought he had secured the points with a late header, only for Umut Bulut to equalise within seconds.
Manchester United and Shakhtar Donetsk remain locked together on four points at the top of Group A after their 1-1 draw at the Donbass Arena with Bayer Leverkusen having closed the gap with a last-ditch 2-1 victory over pointless Real Sociedad.
Simon Rolfes put the Germans ahead on the stroke of half-time and although Carlos Vela cancelled out his effort six minutes after the break, substitute Jens Hegeler curled home a brilliant stoppage-time free-kick to win it.
In Group D CSKA Moscow drew level on points with Manchester City after beating Viktoria Plzen 3-2 in St Petersburg.
Plzen keeper Matus Kozacik's error allowed Radim Reznik's 78th-minute back-pass to slip under his foot, and it proved to be decisive.
There were no such difficulties for Group C leaders Paris St Germain or Olympiakos as both clubs eased to 3-0 victories.
Star striker Zlatan Ibrahimovic claimed a double either side of defender Marquinhos' effort as PSG wrapped up the points against Benfica inside the opening 30 minutes.
But Olympiakos frontman Kostas Mitroglou went one better as he plundered a hat-trick to see the Greeks past Anderlecht in Belgium.
Mitroglu opened the scoring after 17 minutes, and then found the back of the net again 11 minutes after the restart before completing his treble with 18 minutes remaining.