Hamilton got off the line at the same time as the other cars but immediately fell behind, dropping to sixth before the first corner. Rosberg, who started second, took the early lead and cruised to his seventh win of the season, second straight this year and first of his career at the storied Monza circuit, which has hosted more Formula One racing than any other track.
Rosberg also cut Hamilton’s championship lead to two points with seven races remaining.
Hamilton climbed his way back to finish second.
“Obviously the start wasn’t great but it’s still a great day for Mercedes Benz and I’m glad to be a part of it,” Hamilton said. Ferrari’s Sebastian Vettel and Kimi Raikkonen crossed third and fourth, respectively.