Beñat San José's side dominated at Vallecas, with De Frutos opening the scoring in the 35th minute before adding a second shortly after the interval. Unai López completed the victory with an excellent strike in the 73rd minute, as Rayo secured three important points and inflicted Celta's first away league defeat of the season.
Giráldez made little attempt to disguise his disappointment, particularly with the way his team defended.
“We defended badly and when you do that, you leave with three goals conceded, and it could have been four because Radu made a very good save. We lost too many situations involving direct play and duels, and allowed Rayo to run, which is what they do best. Defensively, we were very poor.
“We had some good moments in possession and opportunities to create more, but we leave with a very bad feeling because you have to take advantage of the opportunities the game gives you and create much more danger.”
The Celta Vigo manager also accepted personal responsibility for a performance that fell short of his expectations.
“We have suffered a heavy defeat and must reflect on it. The level we showed today is not acceptable. The first person responsible is obviously me. When you don't show the intensity required in a professional match, never mind in the Primera División, opponents will create danger against you.”
San José, meanwhile, was delighted with Rayo Vallecano's response after their previous disappointment against Elche, praising the quality and patience shown by his players.
“We are very happy. We played a very complete match. That way of starting is very much who we are. Today we had that freedom on the ball, and although sometimes you are more accurate than at other times, today we built our attacks with great patience. We chose the moments very well.
“I am very proud of keeping a clean sheet. Celta are a team who attack a lot and concede very few goals. We saw the Rayo we need to be. It was important to play at this level. I congratulate my players wholeheartedly.”
The Rayo coach also singled out De Frutos, whose two goals rewarded his consistency and importance to the team.
“He is very familiar with scoring goals. I am very happy for him and he is very necessary for us. He is extraordinary, professional and very humble. He deserves it because of his consistency. He is fundamental to us. I told him how happy I was for him. He deserved to experience a match like this.”
Giráldez acknowledged that his side had failed to take advantage of the opportunities available, but insisted the defeat should provide a lesson.
“We have had a difficult defeat and we have to reflect. We cannot accept the level we showed today.”
San José was equally pleased with the atmosphere at Vallecas, thanking supporters for their backing and believing the connection between the club and its fans was improving.
For Rayo, the victory offered a welcome response and a performance that San José believes can provide a foundation for further progress.