The second straight home win lifted the Milan side to 73 points, three clear of Juventus which is at Lazio in today's matches of the 33rd round.
Milan's success was likely to put additional pressure on Juventus, coming off a home loss to Inter Milan and missing several key players, including strikers Zlatan Ibrahimovic and David Trezeguet, for the match with Lazio.
Brazil's Kaka kicked in the opening goal at San Siro following a series of rebounds in the 33rd minute.
Tomasson, fed by Andriy Shevchenko, made it 2-0 on a quick counterattack and Brazilian defender Cafu netted Milan's third goal with a right-foot volley in the 70th minute for his first tally this season.
Park Ji-sung scored one goal and set up another as PSV Eindhoven clinched the Dutch premier league title with a 3-0 victory over Vitesse Arnhem.
With four games left to play, PSV's 17-point lead over defending champion Ajax Amsterdam in the Eredivisie is unassailable, and Eindhoven can focus on its Champions League semifinal matches against AC Milan.
In other league games, AZ Alkmaar lost 2-1 at RKC Waalwijk, cementing its position in third place, one point behind Ajax. Roda JC Kerkrade overpowered ADO The Hague 4-1.
RSS