Ronaldo, who won the European Golden Shoe last season after netting 40 times in the League, netted in the 24th, 71st and 87th minutes to complete yet another treble for Real — the Portuguese forward scored at least three goals in a competitive match seven times last term.
Marcelo, Xabi Alonso and Kaka were also on the scoresheet for Jose Mourinho's men, who but for some fine saves from the Zaragoza goalkeeper Roberto Jimenez and some indifferent finishing would have been celebrating an even bigger victory.
The triumph was the perfect start to the season for Real, who finished runners-up to Barcelona last term. Three-time reigning champions Barca begin their campaign at home to Villarreal tonight.
Alvaro Negredo was the star at the Ramon Sanchez Pizjuan as he scored both of Sevilla's goals in an impressive 2-1 home win over big-spending Malaga.
The Spain striker took just 90 seconds to open his season's account before a second expert finish on 26 minutes proved enough, despite Santi Cazorla's late free kick for Malaga.
Negredo could have scored even scored more but, after Sevilla crashed out of the Europa League to Hannover in midweek, his double ensured a morale-boosting success over their Andalusian rivals.
New-look Atletico Madrid began their campaign with a disappointing goalless draw at home to Osasuna.
The Rojiblancos, who this summer sold last season's top scorer Sergio Aguero to Manchester City and look set to see Diego Forlan depart the club in the coming days, were without record signing Falcao and were unable to break down Osasuna despite dominating at the Vicente Calderon.
Promoted Rayo Vallecano claimed a creditable point in their first game back in the Primera Liga after drawing 1-1 at Athletic Bilbao.
After a lacklustre first half the game burst into life in the second period with two goals in five minutes. Athletic went in front on 55 minutes when Ander Iturraspe netted but Rayo responded immediately and drew level thanks to a fine finish from Jose Maria Movilla.
It also finished 1-1 at the Coliseum Alfonso Perez as Getafe coach Luis Garcia saw his new team share the points with the side he managed last season, Levante.
Hosts Getafe took the lead with a wonderful team goal scored by Miku in the 62nd minute but Levante responded well and equalised 13 minutes from time through Juanlu.
Real Mallorca got their season off to successful start with a comfortable 1-0 win over Espanyol at the Iberostar.
Jonathan De Guzman scored the only goal of the game with a deflected effort half an hour from time in a match between two sides confident in possession but failed to provide a potent goal threat.