Valencia twice led at the Bernabeu before Ronaldo stabbed the ball home with a deft backheel two minutes into five added on.
Barcelona's draw and Atletico Madrid's defeat left the door wide open for Madrid but they struggled to push through it as the top three all dropped points on the same weekend for the first time this season.
After Ronaldo levelled, both he and substitute Alvaro Morata had golden chances for a winner but missed the target.
"La Liga is a tough division, as it always has been. It will be decided in the last few games, like I've always said. It has been a tough matchday for all three teams at the top of the league and now the championship is more open than ever," said Real coach Carlo Ancelotti afterwards.
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