La Liga leaders Barca dropped points against relegation-threatened Las Palmas, who earned a 1-1 draw after Jonathan Calleri's penalty cancelled out Lionel Messi's 21st-minute opener.
Las Palmas were gifted the opportunity to equalise following the break when referee Antonio Mateu pointed to the spot, with Barca head coach Ernesto Valverde lamenting the "invisible penalty" post-match.
The result saw Barca's lead over second-placed Atletico left at five points and Busquets said: "We've dropped two points [against Las Palmas] in an important moment.
"But we knew that it was a difficult ground to come to, even though they're in the bottom three.
"Sunday's game against Atletico will be the tougher battle.
"We are in a privileged position in La Liga and we're going to try and keep it that way with a win this weekend."
On the penalty incident in the 48th minute, Barca team-mate Andres Iniesta added: "I didn't see the penalty, but the referee referred to possible hands.
"It is a contrary situation, as the [Las Palmas] goalkeeper's handball outside the area before half-time was very clear, but we can't change the result now.
"We leave with a bittersweet sensation, because we've let two points go. We lacked that final pass in the final third and we weren't able to build a bigger lead when we got ahead."
Undefeated Barca welcome Atletico to Camp Nou on Sunday.