Ronaldo came into this match without a league goal this term but had hit two in the Spanish Supercopa series against Barcelona and opened his Primera Division account as he netted after 26 minutes from a tight angle.
And he made it 2-0 early in the second half after his initial attempt was saved by Granada goalkeeper Tono, to take his tally to 150 since signing for the club in the summer of 2009.
The former Manchester United winger is 10th in the club's all-time scoring charts, having netted 33 in 2009-10, 53 in 2010-11 and another 60 last season. He now has four in all competitions this term.
Ronaldo went off with a thigh injury after 63 minutes.
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