Born in Les Franqueses del Vallès, Barcelona, Catalonia, Sergi was a youth product of giants FC Barcelona. He had not yet appeared in La Liga when he was summoned by first-team manager Johan Cruyff to a UEFA Champions League group stage game away against Galatasaray S.K. (0–0, on 24 November 1993), and from then on became the side's undisputed first choice, never playing less than 31 matches until 1999; with "Barça" he won three leagues, two cups and two supercups, adding the 1997 edition of the UEFA Cup Winners' Cup and the subsequent UEFA Super Cup, partnered in the other defensive wing by another youth graduate, Albert Ferrer.