Thibaut Courtois expressed his frustration at Real Madrid conceding "too many silly goals" after falling to their first LaLiga defeat of the season in a 3-2 loss at Rayo Vallecano.
Santiago Comesana netted a fifth-minute opener on Monday against Madrid, who have kept just two clean sheets in their first 13 LaLiga games, their lowest tally at this stage of a season since 2013-14.
Luka Modric's penalty and Eder Militao's header gave Madrid the lead before Alvaro Garcia's first-half equaliser, and Carlo Ancelotti's side were left frustrated by a contentious Oscar Trejo winner after the interval.
Trejo scored a retaken penalty after Dani Carvajal was penalised for encroachment following Courtois' initial spot-kick save, but the Madrid goalkeeper acknowledged his side were far from their best after the defeat.
"Rayo are having a great season, we knew it was going to be difficult, and we weren't up to the task in the first half," the Belgium international said.
"We conceded too many silly goals, due to mistakes or not being 100 per cent in the match.
"Then the penalty, bad luck. The referee told me that because of Carvajal, that's what they told him in the VAR, that he gets into the area earlier.
"Then I wanted to stay in the centre, but I threw myself and I had a better corner than the one I stopped. It's a shame, I saved the penalty and in the end everything changes. I hope it's our only defeat in LaLiga.
"With so many games, it may be normal that we are tired. The draw against Girona was more bad luck. Today was not our best day and Rayo played well."
While Courtois refused to criticise referee Juan Martinez Munuera, Madrid team-mate Lucas Vazquez questioned why the VAR and officials have not been as "rigorous" in other games this season.
"It was a complicated game, they got ahead very quickly, and although we turned it around, they equalised again and that hurt us," Vazquez said.
"It was difficult for us to find our football, and Rayo is a complicated team that today has been very good.
"But they [the referee and the VAR] send Trejo to shoot again and in other games they don't, they should always be just as rigorous."
Madrid trail LaLiga leaders Barcelona by two points and host Cadiz on Thursday in their last game before the World Cup break.