Real Mallorca came from a goal down at half-time to hand Real Madrid a humiliating 5-1 defeat at the Bernabeu on Saturday and leave the reigning European champions just a point clear at the top of the table.
Real last suffered a home league defeat in November 2000, also to Mallorca. The size of Saturday's loss mirrored a 5-1 reverse at home to Real Zaragoza in December 1999.
Yet they had appeared set to extend their lead to seven points when Ronaldo put them ahead after nine minutes in Saturday's match.
Instead, they were left barely clinging on to top spot as Mallorca's extraordinary comeback was followed by a 1-0 win for Real Sociedad at home to Sevilla, Xabi Alonso heading in the only goal after 31 minutes.
With six games left to play, Real Madrid lead the standings with 64 points, followed by Real Sociedad on 63.
Deportivo can join Sociedad on the 63-point mark if they win at home to Recreativo Huelva on Sunday.
Real, who host Juventus in the first leg of their Champions League semi-final on Tuesday, will be glad to see the back of Mallorca, who were the last side to beat them in a league match at the Bernabeu two-and-a-half years and 49 games ago.
"Mallorca were superior to us," Real coach Vicente del Bosque recognised.
"I'm not surprised, though. I have enough experience to see things with a bit of perspective. Virtually nothing surprises me in football."
TURNED SHARPLY
Real took the lead after nine minutes when Ronaldo took a pass from Steve McManaman on the edge of the area, turned sharply and beat Mallorca keeper Leo Franco at his near post. The home side played at a leisurely pace for the remainder of the first-half, hardly bothering to look for a second goal.
Mallorca had started timidly but they roared into life after the break and managed to turn the game around by the 52nd minute.
Walter Pandiani took a loose ball in the area and swept in for the equaliser after 48 minutes.
Real were then hit on the break as Samuel Eto'o managed to slide through a perfectly weighted ball for Albert Riera to convert.
Eto'o scored a brilliant third in the 63rd minute, taking the ball on the right of the area, leaving Roberto Carlos standing with a spectacular change of pace and squeezing a shot past Iker Casillas.
A Roberto Carlos own goal made it 4-1 to Mallorca after 70 minutes and Mallorca's substitute striker Carlos wrapped up the scoring in the second minute of injury-time.
"Football sometimes needs the more modest clubs to join the party," said Mallorca coach Gregorio Manzano.
"We played a very good game today. We managed to control the game and, after a nervous start, our own emotions. That was very important."
