The Briton started the race from ninth on the grid, but struggled to overtake in the final part of the Monza race.
The 33-year-old told Autosport: "Today was tough. I think our pace was better than 10th, but we got stuck behind the Toro Rosso and couldn't overtake.
"The problem was that as soon as the fuel load comes down, the straight-line speed is far greater. As soon as we followed anyone we were in a difficult position.
"We got it wrong with the ratios and it's a problem we will hopefully solve for the next one."
The result leaves Button ninth in the drivers' standings.