Lewis Hamilton won the Italian Grand Prix at Monza with ease, but was made to wait for victory to be confirmed by the stewards after his tyre pressures were found to be below the minimum level at the start of the race.
Hamilton won by 25 seconds from Ferrari's Sebastian Vettel and Williams' Felipe Massa, with Nico Rosberg's retirement on the penultimate lap meaning he leads the championship by 53 points with seven races to go. Despite holding a comfortable lead for much of the race, Hamilton was told to up his pace in the closing laps as the Mercedes pit wall was worried about a possible time penalty, but he was not aware of the reason at the time.
The reason was because FIA had checked the tyre pressures on the left side of the front four cars on the grid ahead of the start of the race and found Hamilton's left-rear tyre pressure to be 0.3 PSI below the minimum pressure of 19.5 PSI set by Pirelli. The left-rear tyre on his Mercedes team-mate Nico Rosberg was found to be 1.1 PSI too low, but Rosberg's race ended two laps before the end when his engine let go while running third. Both Ferraris had pressures in compliance with the regulations. Several hours after the race the stewards upheld Hamilton's victory.
The FIA informed the teams of the potential breach of regulations one hour and four minutes into the race, which was when the Mercedes pit wall gave Hamilton the hurry up. Asked about the pit radio message to his driver, technical boss Paddy Lowe added: "I'd call it an abundance of caution, because we haven't done anything wrong. We thought let's make a gap. We've been summoned to the stewards so we'll go there and explain it."
Before the post-race drama, the Italian Grand Prix had been a fairly dull affair. Ferrari's hopes of causing an upset by beating Mercedes were halved when Kimi Raikkonen's car kicked into anti-stall at the start and he dropped from second on the grid to last place by the first corner. Vettel quickly realised the difficulty of the task of keeping up with Hamilton within a handful of laps had dropped over five seconds off the Mercedes. The two Williamses of Felipe Massa and Valtteri Bottas were third and fourth ahead of Rosberg, who made a slow start and dropped to sixth.
Running a five-race old engine after a problem with his new Monza power unit on Saturday, Rosberg struggled to match the two Williamses for straight-line speed and instead made an early pit stop on lap 18 to gain an advantage on fresh tyres. Once the pit stops had panned out Rosberg emerged comfortably in front of Massa and Bottas and set about closing the gap to Vettel. He got within 1.2s when his engine let go with a lick of yellow flame from the exhaust, much to the delight of the Tifosi lining the circuit.
That promoted Massa back up to third but he had to hold off Bottas at the end. The pair were engaged in a thrilling battle on the final lap as Bottas attacked his team-mate, but ultimately came up 0.3s shy as they crossed the line. Raikkonen battled his way from last place back up to fifth with a series of bold overtaking manoeuvres that showed the strength of the updated Ferrari power unit. at Monza Sergio Perez finished sixth ahead of Force India team-mate Nico Hulkenberg, Red Bull's Daniel Ricciardo and Sauber's Marcus Ericsson, who picked up the final point on offer in tenth.
The victory means Hamilton has the luxury of being able to retire from any two of the remaining seven races and still lead the championship, such is the size of the gap to Rosberg.