At Sampdoria he formed a prolific strike partnership with teammate and childhood friend Roberto Mancini, earning the nickname "The Goal Twins" ("I Gemelli del Gol", in Italian). With Vialli at his best, Sampdoria had the most successful era in its history. They won their first ever Serie A championship in the 1990–91 season, in which Vialli was league top scorer with 19 goals – celebrating many of his goals with a backflip, including one against Inter – one UEFA Cup Winners' Cup (1990) – where he scored both goals in the 2–0 win over Anderlecht in the final (once again finishing the tournament as top-scorer), and three Italian Cups (in 1985, 1988 and 1989), also setting a record of 13 goals in a single edition of the Coppa Italia during his time at the club. They also won a Supercoppa Italiana, and reached the final of the UEFA Supercup, and the European Cup final in 1992, losing to Johan Cruyff's Barcelona "Dream Team" of Spain 1–0.