Real coach Jose Mourinho warned that the opening weekend of fixtures often spring surprises but the game went according to plan for the Portuguese on SUnday and it will serve as a statement of intent for Barca who are in action Monday away to Villarreal.
Ronaldo was the joint highest goal scorer in Spain last season with Lionel Messi on 53 goals and mid-way through the first half he opened up his league account for this campaign after converting a Mesut Ozil pass.
Marcelo quickly added a second as Real peppered the Zaragoza goal. The home side were never in the contest and in the second half Real's domination was reflected in the scoring with Xabi Alonso (63) and Kaka (81) finding the back of the net along with two more goals from Ronaldo after 70 and 86 minutes.
"In order to win you have to play well but I am not going to hide from the fact that my friend (Zaragoza coach) Javier Aguirre has had problems and not been able to count on several important players," said Mourinho.
"At 2-0 the game was already over and so it depended on whether Real Madrid played together or individually and the players chose the first option and we won by a big margin."
A double from Alvaro Negredo saw Sevilla win the Andalusian derby 2-1 against Malaga.
Former Real youth product Negredo headed home in the first minute and was in imperious form against a Malaga side that is looking to push for a place in Europe this season after plenty of investment over the last year.
He was on target again midway through the first half as Sevilla dominated. Malaga's expensive new signings failed to have an impact on the game until Santi Cazorla scored ten minutes from time but it was only to be a consolation.
Earlier, an unfamiliar Real Mallorca side scraped a 1-0 win over Espanyol thanks to a deflected Jonathan De Guzman goal.
There were five new faces in the Mallorca starting line-up and it was one of those, Alejandro Alfaro, who had the side's best chance of the first half in the opening minute.
Espanyol grew as the game went on and after the break youngster Alvaro Vazquez hit the post and saw another effort well saved.
The visitor's lack of strength in attack proved crucial as a messy goal from De Guzman, which hit a defender and wrong-footed the goalkeeper, decided the encounter.
"This was a typical game for the start of the season and we won it through a bit of luck," admitted Mallorca coach Michael Laudrup.
"We played well in the first half considering that we had so many new players in the starting line-up. We lacked a bit of rhythm but it is fantastic to have picked up three points."
Espanyol coach Mauricio Pochettino was disappointed and accepted that the loss of players like Pablo Osvaldo and Jose Callejon had made a difference to the team.