Mercedes had another difficult weekend at Monza, where Ferrari was clearly a step ahead and the W14 was the third-fastest car.
George Russell and Hamilton eventually finished fifth and sixth as they showed an obvious top-speed handicap.
Hamilton's life has been made harder of late by a couple of difficult qualifying sessions, with the seven-time champion starting only 13th at Zandvoort and eighth at Monza.
While on both occasions he has moved up the order and scored decent points, his team has not been leading the chase of pacesetter Red Bull.
"Races are pretty straightforward for me," he said. "I've just got to do better in qualifying, so it's not such a difficult day.
"And just living with the car that we have at the moment. Today is the third fastest car, and it's obviously painful for all of us. We wish we were quicker. But we're just counting down the days until February."
For the second consecutive race Hamilton went for an offset starting tyre strategy in Monza, and he was just one of three drivers to go for the hard compound in his first stint.
Source: Autosport