Real cut the lead on their arch-rivals back to five points with two games left to play, which means Pep Guardiola's Barca side can wrap up their third consecutive league crown with a draw in their game in hand at Levante on Wednesday.
GEAR:Save £10 onRonaldo shirts with Kitbag. Free delivery on orders over £50
Champions League finalists Barca have 91 points to Real's 86 and hold the head-to-head advantage over Jose Mourinho's team should they finish level on points next week.
Deportivo La Coruna's 2-1 comeback win over Athletic Bilbao pulled them out of the bottom three up to 14th with 42 points.
Ronaldo closed to within two goals of Real Madrid's club record of 38 for a season, held by Hugo Sanchez, with his seventh goal in four days ahving bagged four in Saturday's 6-2 demolition of Sevilla.
The Portugal forward outjumped two defenders to head the opener in the 24th minute from Mesut Ozil's superb curling cross with the outside of his left boot.
The German playmaker also laid on Ronaldo's second after a swift counter-attack in the 57th.
Substitute Karim Benzema then guided in Xabi Alonso's long pass before Ronaldo sealed his hat-trick with a penalty in added-time, taking his league tally for the season to an unrivalled 36 goals, ahead of Barcelona's Lionel Messi with 31.
"I'm in good form. I am fighting to win the top scorers' award but I am not obsessed with it," Ronaldo told Spanish television.
Both teams walked out at the Sardinero stadium with shirts dedicated to Ballesteros, while a group of children carried a giant photo of him into the centre circle, for a minute's silence before kick-off.
