He missed a penalty after the break, and Dani Parejo, who gave the spot-kick away, equalised inside the final 10 minutes.
After the quick start to the match, the pace dropped, with neither team seemingly interested in sending men forward.
Karim Benzema sent a tame header into the arms of Diego Alves, but otherwise, the Valencia stopper was barely troubled.
The Frenchman tried his luck again after 21 minutes, with Alves intervening, before Ronaldo opened the scoring thanks to some shoddy defending.
The final opportunity of the half fell to Los Che, with Munir El Haddadi bending a shot toward goal that was easily saved by Navas.