Carlo Ancelotti was at a loss to explain his team's sudden dip in form after Espanyol claimed a deserved 2-1 win in La Liga on Sunday to extend Real Madrid's winless run to three matches.
Real Madrid, who suffered a shock defeat to Moldovan minnows Sheriff Tiraspol in the Champions League on Tuesday, had the chance to move ahead of city rivals Atletico Madrid at the top of the standings but slumped to their first La Liga loss of the season. After eight matches, Real and Atletico are level on 17 points.
Espanyol took the lead on 17 minutes at the RCDE Stadium in Catalonia when Raul de Tomas, a former Real Madrid youth player, found the net.
Aleix Vidal scored a sparkling second goal after nutmegging Nacho and smashing the ball past Real goalkeeper Thibaut Courtois 15 minutes into the second half.
French striker Karim Benzema continued his fine start to the season by halving the deficit with his 10th goal in all competitions, but Espanyol managed to navigate the final 19 minutes to secure victory.
After a goalless draw at home against Villarreal in their previous league outing, Real have now gone three games without a win having started the season with five wins and a draw in their first six league matches.
"[It was] our worst match of the season," Real Madrid manager Ancelotti said. "We played badly.
“It wasn’t an accident today and we deserved to lose. The reaction came too late. We started with one defensive and offensive idea, but we couldn’t keep a sense of calm or maintain that idea after conceding.
"There was confusion on the pitch and we weren’t well-positioned, with or without the ball.
"Now, we have the international break, but sometimes you want to play again straight away. We have to see what happened, how the team changed its attitude in one week.”
The result gave Espanyol their second win of the season and ended a run of four successive defeats against Real Madrid. Their most recent victory over Los Blancos came in February 2018, but prior to that, Espanyol had lost all but three matches - all of them draws - dating back to October 2007.
"They are a spectacular rival in every way. We have suffered against them in the past and to beat them you must also suffer," Espanyol manager Vicente Moreno said.
"We had to play a perfect game but we could have improved in some aspects to be calmer in the final stage."
Goalscorer De Tomas, 26, spent his entire youth career at Real Madrid, coming through the ranks to play for their reserve team Castilla. However, he left the club before making an appearance for the first team and after loan spells elsewhere in La Liga and a brief stint in Portugal with Benfica, he joined Espanyol last year for a club record €20 million.
It has proved money well spent so far, with De Tomas averaging roughly a goal every other game and the Spanish striker said he was delighted to contribute to Espanyol's victory against his former side.
"We gave a tremendous effort. A rival like Real Madrid demands a lot from you," he said. "I have a Real Madrid past, but I give everything to help my team. I am happy for the goal and I wish Madrid luck for the rest of the season."