Ronaldo's second goal came from a fearless diving header but the Portuguese took a boot to his head and fell to the ground in agony.
With the big win, Real Madrid have returned to the fourth position in La Liga ahead of Villarreal.
Prior to this game, Real Madrid's bad second half record was well known.
BC-SOC-Spanish Roundup, 1st Ld-Writethru, 364Blood, goals for Ronaldo as Madrid scores 7 to end poor runAP Photo FS113, FS125, FS120, FS104, FS105, FS106, FS103, FS114Eds: Updates with detail.
Luka Modric added another and Cristiano Ronaldo contributed two late goals to put a spring back into Madrid's step.
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Ronaldo was caught by defender Fabian Schar when diving to head home Madrid's sixth goal of the rout, forcing him to temporarily leave the pitch with blood streaming down his face.
Bale admitted to some frustration at having to mostly watch on as La Liga leaders Barcelona built up their current 16-point advantage in the table. The Portuguese striker, well known for the care he takes over his physical appearance gave us a curious image in the 83rd minute of the game.
Ronaldo, who won the Ballon d'Or title five times, is unhappy with the current club Madrid's failure to make promises made under the new agreement.
"We're without two centre-backs at the moment and I'm not happy about it".
"We'll just keep working hard to win games and do as best we can". We need to secure Champions League football which is important first, and then we need to grow in confidence.