If Real had failed to win, victory for Barca against Real Betis at the Nou Camp on Sunday would have secured a fourth title in five years as they would have been at least 13 points clear with only four games left and 12 points available.
Jose Mourinho's Real side are refusing to relinquish their league crown without making it as difficult as possible for their bitter rivals in the final weeks of the campaign even if they gave up on the title several months ago after a poor start.
"We will keep working," Real's Portugal defender Pepe told Spanish television.
"We know that it's a tough ask but we represent a very important club and we will honour the shirt to the end."
Valladolid struck back almost immediately when Javi Guerra finished off a swift breakaway in the 35th minute and Kaka restored Real's lead four minutes after the break.
Ronaldo looked to have killed off the game 20 minutes from time when he headed home from a corner, the Portugal forward's 33rd league goal of the campaign.
Real's victory lifted them to 77 points from 34 matches, eight behind Barca and eight ahead of third-placed Atletico Madrid, who were held to a 0-0 draw at Deportivo La Coruna in the late kick-off.
Valencia stayed in the hunt for a Champions League berth with a thumping 4-0 win at home to nine-man Osasuna but Malaga's hopes of a return to Europe's elite club competition faded when they lost 1-0 at Granada.
Osasuna's miserable afternoon was completed when David Timor picked up a second yellow card 15 minutes from time and Jonas made it 4-0 from the penalty spot in the fourth minute of stoppage time after a handball in the area.
Valencia are fifth on 56 points from 34 of 38 matches, two behind Real Sociedad, who occupy Spain's fourth and final Champions League spot.
After outperforming on their Champions League debut by reaching the quarter-finals this season, Malaga's defeat leaves them in sixth, three points behind Valencia and fo
