The Italian was jubilant after watching his side leapfrog the Catalans into second place in La Liga and revealed defender Sergio Ramos will return for the Copa del Rey final.
The Catalans lost for a second time in a week, on the back of their Champions League quarterfinal exit, with Madrid taking advantage in ruthless fashion to breathe new life into its title bid.
Goals from Angel Di Maria, Gareth Bale, Isco and Alvaro Morata moved los Blancos level on points with Atletico Madrid, which plays on Sunday, with Ancelotti predicting more twists and turns ahead.
He told reporters after the game: "I was a little surprised by Barcelona's defeat, but everyone is fighting for their goals at the moment.
"Barcelona believe they can still win the league. There will be many surprises and they will fight until the end."
Madrid will hope to heap more misery on Barca when the two sides meet in the Copa del Rey final on Wednesday night, though Ancelotti is not convinced Saturday's results will have an impact on the game.
"The Italian also gave an update on the fitness of Sergio Ramos - who was missing from the matchday squad completely on Saturday - and Cristiano Ronaldo.
"I don't think Barcelona's defeat will have an impact on the Copa del Rey final," he added. "I think Ramos will be able to play on Wednesday. He had a neck problem but should be back. Cristiano still depends on how he progresses. Marcelo won't play."