The free-scoring Portugal forward was pipped to the Ballon D'or by old foe Lionel Messi for the fourth time in a row on Monday, but did what he does best on Wednesday as Madrid turned around a 1-2 deficit.
Ronaldo got them going in the third minute, cutting in and swerving a shot across goal and beyond the perplexed Sergio Alvarez.
He made it two in the 23rd minute, volleying in Luka Modric's chip over the top, with his hat-trick coming three minutes from the end as he made good of Gonzalo Higuain's pass.
Sami Khedira made it four, with Sergio Ramos' sending off the one black spot for Madrid.
Sevilla, who were already 5-0 up against Real Mallorca, were afforded the luxury of taking it easy on Wednesday, with a 2-1 defeat doing no harm.
They actually led through Manu del Moral's 22nd-minute opener, but half-time substitute Thomas Brandon and Alejandro Alfaro at least earned Mallorca a win on the night after the break.
In Wednesday night's other game, Real Zaragoza turned a 1-0 first-leg lead over Levante into a 3-0 aggregate win, Franco Zuculini and Paco Montanes on target as the visitors had Hector Rodas sent off.
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