Real went into Sunday's 'Clasico' against Barcelona as La Liga leaders, having won 10 of their previous 12 games, but just as they did at the Nou Camp earlier in the campaign, Ancelotti's men slipped to defeat at the Bernabeu.
The 4-3 reverse meant Real surrendered top spot to Atletico Madrid who also have a win and a draw from the two league meetings with their city rivals this season.
"I am not happy with this," Ancelotti told a news conference. "It is difficult to explain as Real are one of the strongest teams in the world and we will continue to show this until the end of the season.
"In the first game against Atletico we deserved to lose and then in the first half against Barcelona we didn't compete well but since then the last two games, away to Atletico and then in Sunday's match, they were even."
A victory for Real against Barca would have put them firmly in the driving seat to win the title. Now they must lift themselves again for Wednesday's tricky game at Sevilla who have won their last five league matches.
"It is not a case of looking for who was responsible, or to blame for the defeat," said Ancelotti. "It came after a lot of matches where we didn't lose.
"In football you cannot always explain everything by looking for the culprit. The team was fine before the loss and it will be afterwards.
"We have the same number of points as Atletico and one more than Barcelona. Tomorrow's game will be important for us to respond," said Ancelotti.
"We played well (against Barca) and there were only a few small errors. The mentality was good and we had chances to win.
"I think Real left the game not happy but with a positive attitude."
Barca coach Gerardo Martino said he was now looking for consistency from his side, starting at home to Celta Vigo on Wednesday.
"The result at the weekend has put us back into title contention," he added. "Now we have to play well against Celta and in the remaining games of the season.
"We cannot make mistakes. We are trying to play at the top level and to play like we did at the weekend but I don't have a way to guarantee it.
"The league, the Champions League and the (King's) Cup are now in their final stages and if we don't have the right intensity and rhythm in each game then we put at risk the chance of winning the titles," said Martino.
"The main point is the consistency and if we had been more consistent then we would now be in a better position."
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