By Andrew Benson
BBC Sport at Monza
Hamilton finished seventh at a rain-soaked Monza after qualifying in 15th
Lewis Hamilton said he may have won the Italian Grand Prix had he switched to intermediate tyres at his first stop.
The McLaren driver finished seventh after starting 15th and said the race was a "missed opportunity" for him and title rival Felipe Massa.
The Brazilian cut Hamilton's lead to just one point by finishing sixth.
"I showed great pace and think a win was possible," Hamilton said. "If I'd chosen intermediates at the first stop, I'd have finished further up."
Hamilton described the result as "not that bad" and said he viewed the race as damage limitation after a wrong choice of tyres in qualifying led to him failing to get out of the second knock-out session.
Massa finished in the same place he started and his Ferrari team-mate Kimi Raikkonen, who was one place ahead of Hamilton on the grid, could manage only ninth.
The Finn is now 21 points behind Hamilton with a maximum of 40 available in the remaining four races in Singapore, Japan, China and Brazil.
"I had a great race," the Englishman said. "But considering I overtook eight people and Kimi didn't do all that much… it's a bit of a shame, but I still came away with my world championship lead intact."
Driving through the pack, passing Kimi and leaving him behind… it was a great feeling.
Hamilton, 23, said he was "more relieved than anything" that he had not suffered more damage in the championship.
"I'm not surprised because I drove my arse off and you know what I can do in the wet," he said. "I had no doubts in my mind - I knew I could do a good job."
Asked to compare his performance at Monza with his other great wet weather drives in the British Grand Prix in July and last year's Japanese race, Hamilton said: "It's probably right up there.
"Driving through the pack, passing Kimi and leaving him behind… it was a great feeling. And I'm really happy that I was able to pass so many cars."
Hamilton drove superbly in the wet conditions in the first part of the race and was running second behind eventual winner Sebastian Vettel when he had to come in for fuel and tyres on lap 27.
That was only a lap before David Coulthard became the first significant driver to switch to the intermediate tyres, which are less grippy on a wet track than extreme wets but more effective as it dries.
BMW Sauber's Nick Heidfeld and Renault's Fernando Alonso then switched to the tyres on lap 29 and lap 30.
Had he switched to intermediates at his first stop, when the weather forecast was for more rain, Hamilton would not have had to stop again.
He rejoined from his stop 33 seconds behind Vettel, with the Toro Rosso still having to make another stop for fuel and intermediate tyres.
Whether Hamilton could have won is a moot point, as he ran into problems with his intermediate tyres a few laps after eventually fitting them on lap 36.
But they would have been less prone to the problem he encountered - graining, when the tyre rips across its surface - had he run them for a few laps in wetter conditions first.
McLaren boss Ron Dennis said the team had had to weigh up not only how much grip Hamilton would have but also how long the tyres would last - there were still 26 laps to go when Hamilton made his first stop.
Dennis said: "The decision wasn't just about getting on to them. It was about making them last.
"So we had to be very sure they were quicker before putting him on to them."
Hamilton now has an anxious wait before the sport's governing body, the FIA, hears McLaren's appeal into the penalty that deprived him of victory in the Belgian Grand Prix.
McLaren go before the FIA court of appeal in Paris on 22 September to argue that he should not have been docked 25 seconds for gaining an advantage by cutting a chicane while racing Kimi Raikkonen in the closing stages of the race.
"We are in both championships," Dennis said. "We lost one point in the drivers' but took a lot of points in the constructors' [thanks to Hamilton's team-mate Heikki Kovalainen's second place at Monza].
"We don't know how it will go next week in Paris. But if we had those points we would be leading the constructors so we'll just have to see how it goes."