FC Barcelona midfielder Pedri lamented a limp display on Sunday as the Catalans lost 1-0 to Leganes in La Liga.
Rayo Vallecano did Barca a massive favour by holding Madrid to a 3-3 stalemate 24 hours previously.
Rather than take advantage of the chance to go three points clear at the summit, however, Barca wasn't able to come back from a Sergio Poirrier goal on four minutes and slumped to a second consecutive home defeat.
Reacting to the setback, Pedri remarked that it was a "f*cked up game, to be honest".
"It is impossible to leave happy today. I think we started a little asleep, they scored that goal against us. And then we woke up, we created chances, but we lacked spark," the playmaker added.
"We have to get into the games better," Pedri demanded. "When a team like that scores quickly, they put a lot of people behind [the ball]. And we lacked the spark I said and clarity in front of goal. We're on a bad run and we have to improve."
Pedri conceded there are "many games" to play in soccer these days, but stressed that it "is not an excuse".
"We're well prepared and we arrive well for the games, but we have to arrive and finish with the same confidence with which we do in the Champions League. If you don't score it's impossible to win, and we have to improve that," Pedri concluded.
Pedri's teammate Alejandro Balde, who was one of few Blaugrana starts that played with anything even remotely resembling intensity, said to Esport3 that Hansi Flick's men "should have left with the three points".
"There's no choice but to learn from mistakes and work to improve it," the left back added.
"Conceding a goal so quickly is always difficult, because it's a hard blow," Balde continued. "But I think we knew how to react, the only thing we lacked was to create chances. We haven't had good results in La Liga this month, but we have to focus on ourselves and not look at the rest and work on our own".