Gattuso was bought by Milan for €8 million from Salernitana in the summer of 1999. He made his debut with the club on 15 September 1999, in a 0–0 away draw with Chelsea in the UEFA Champions League; he soon broke into the starting line-up that season, also playing his first Milan-derby match on 24 October 1999, in which he stood out and immediately endeared himself with the Milan fans for the maturity and tenacity he demonstrated when facing Inter striker Ronaldo, who was widely regarded as the best player in the world at the time.