Sacchi rejoined his former club on Monday after resigning as coach of Italy's national team. The victory gave the Norwegians second place in Group D of the Champions' League, behind Porto, and a quarter-final tie against the defending champions, Juventus.
The forward Harald Brattbakk put Rosenborg in front in the 29th minute. The French striker Cristophe Dugarry scored Milan's equaliser in the 45th minute but fans jeered Milan players - and goalkeeper Sebastiano Rossi in particular - at the end of the match.
The Norwegians completed the qualifying round with nine points, two ahead of Milan, who could have qualified with a draw. The Rosenborg striker, Steffen Iversen, is due to join Tottenham this week but the Norwegians may now try to keep him at least until March.
n Fifa, world football's governing body, is set to confirm the sport's worst-kept secret on Saturday when it formally announces that Japan will host the World Cup final in 2002. It will also confirm that South Korea, jointly hosting the tournament with their Asian neighbours, will stage the opening match of the finals in six years' time.