Bottas took over the attack on Leclerc and, on fresher tires, kept gaining but locked up with two laps remaining, paving the way for an emotional win for Leclerc, who recorded the first victory of his F1 career at last weekend's Belgium GP.
"Winning here is just a dream", continued the victor, switching to fluent Italian to address a crowd cheering a fitting triumph on the 90th anniversary of both Monza and Formula One's most glamorous team.
After the race, Vettel was asked if he had lost any love for Formula One.
"Thanks to everybody. I have no words".
With Bottas finishing second, Hamilton - who set the fastest lap - only dropped two points to his team mate and nearest championship rival to sustain a 63-point gap at the top of the driver standings.
"It feels fantastic", said Leclerc. "I think I've grown a lot since the beginning of the season". I did the best I could. The driver was unable to set a lap time in Q3 following the freaky incident in qualifying when everyone tried to go slowly, and admitted he just didn't have the straight line speed, but also felt his race pace was improving. "There was a rule put in place and then it wasn't abided by today".
Another short VSC period followed when Daniil Kvyat pulled off on lap 31, his Toro Rosso smoking.
His spin at the Ascari chicane cost him his race and brought him a penalty for re-joining in a risky manner when he collided slightly with Lance Stroll's Racing Point. Hamilton, with nothing to lose, swapped to soft tires and chased the fastest lap, seeking an extra point. In the Constructors' Championship, Mercedes leads with 505 points versus the 351 of Ferrari and 266 of Red Bull.
Sebastian Vettel faces a possible one-race ban after his newest blunder on one other depressing afternoon for the four-time world champion.
A driver is automatically banned for one race if they accumulate 12 points in that time span.
"I think since Austria it is clear you can go a bit further in the way we defend and overtake and the aggressiveness of us drivers", said the Monegasque.
"I can't be happy with my day today", he said. Awesome drive by Daniel Ricciardo too.
Stroll would be punted off the circuit by Vettel with both suffering front wing damage as a result, before Stroll performed a similarly unsafe return to the track in front of Pierre Gasly who was forced into the gravel trap.