Barrichello, 37, is the circuit's oldest active driver and Sunday's victory helped him gained ground in the overall F1 standings with four races left in the 2009 season.
"(The victory) felt great and I have no big words for that," the Brazilian said after winning at Monza for the third time in his career. "The team has done a fantastic job. The strategy was great."
In the updated standings, Barrichello, who drove for Ferrari when he won the race in 2002 and '04, trimmed Button's lead from 16 to 14 points.
Kimi Raikkonen was third, Adrian Sutil fourth, and Fernando Alonso fifth.
Button, Barrichello, Sebastian Vettel and Mark Webber are the only drivers left in the championship race.