Lionel Messi 54th-minute penalty briefly restored parity for the Catalan giants, but Francisco Alcacer's strike five minutes later proved decisive.
Victory for Real Madrid and Atletico Madrid tomorrow would see Barca slip to third in the La Liga standings, and Busquets admits that his teammates chose a bad time to surrender their unbeaten home record in the league this season.
"It has been a long time since we lost here," he told reporters after the game. "It's a slip at a bad moment. It's a pity, we had our chances."
Atletico host Real Sociedad at the Vicente Calderon Stadium tomorrow, before Real travel away to Athletic Bilbao.