Due to injuries and suspension, Guardiola had only one senior defender - Eric Abidal - available for the visit of a Villarreal side that finished fourth last season and had only lost once on their previous three visits to the Nou Camp.
That led to Guardiola employing midfielders Sergio Busquets and Javier Mascherano in a three-man backline, and the Barca boss admitted: "It was a risk to play like that, because we hadn't prepared too much.
"We explained two or three ideas to them, and once again they've shown themselves to be very good and intelligent players. It's the job of the coach to know his players and their qualities. With other types of defenders we would not have been able to play like that.
"To play with three defenders against Nilmar and (Giuseppe) Rossi is always dangerous, but things went well."