Ronaldo missed a penalty and Walter Samuel and Michel Salgado were both sent off as Real Madrid lost 1-0 at Espanyol on a night of self-inflicted misery at Madrid on Saturday.
Three days after a humiliating 3-0 defeat by Bayer Leverkusen, Real went behind to a 42nd minute goal from Maxi Rodriguez but missed a chance to equalise early in the second half when Ronaldo's spot kick was turned away.
Samuel, the Argentine centre-back signed for 25 million euros ($30.45 million) from Roma, received a second yellow card in the 74th minute and Salgado followed him off in injury-time after landing an elbow on Ivan de la Pena.
Victory for Espanyol gave the Barcelona-based club seven points from three games and a three-way share of the provisional lead, with seven matches to be played on Sunday.
Valencia joined them at the top with a 3-1 win at home to Real Sociedad. Marco Di Vaio scored the opening two goals for the champions and Mista added a third before Mikel Arteta pulled one back from the penalty spot.
Osasuna also have seven points after edging past Real Betis 3-2.
Real, who had eked out 1-0 wins in each of their first two league games, slipped to sixth on six points.
Atletico Madrid and Barcelona, the only two sides still with maximum points, square up in Madrid on Sunday.
With Zinedine Zidane and Luis Figo missing through injury, and Raul and David Beckham dropped from the starting line-up, the nine-times European were desperately short of ideas against a confident Espanyol side.
Michael Owen never hinted at marking his first start with a goal and the England international striker made way for Fernando Morientes just past the hour mark.
By that time, Real were already looking down and out.
Raul Tamudo should have scored after 28 minutes when he was put through on goal but the Spanish striker's shot was bundled away.
Second-choice keeper Cesar, playing after Iker Casillas dislocated a finger in the warm-up, was adjudged to have pushed Tamudo at the resulting corner and the referee awarded a penalty.
However, Cesar saved from Tamudo, then repeated the feat when the referee ordered the penalty retaken, and Espanyol continued to press, making the breakthrough three minutes before the break.
With Roberto Carlos way out of position, Dani was able to win the ball on the right of the area and his cross was met by a powerful Maxi header. Cesar saved the first attempt but with no covering defender Maxi was able to turn in the rebound.
Real were given a route back into the game when Ronaldo was brought down after being put through by Guti but Espanyol's Cameroon goalkeeper Carlos Kameni saved the Brazilian's effort to his left.
Espanyol could easily have scored half a dozen more as Real showed the same defensive weaknesses as in the Champions League in midweek but poor finishing and heroics from Cesar -- who was forced to play through a knee injury -- kept the home side at bay.
"We are clearly nervous at the moment," said Cesar. "We have to control the ball and get back to playing our game. That's the way to win."