Lewis Hamilton and Max Verstappen were involved in their second major incident of a seismic F1 title rivalry on a day when McLaren won a grand prix for the first time in nine years
Daniel Ricciardo took the chequered flag in an astonishing Italian Grand Prix for his eighth F1 win, and first since the Monaco GP of 2018.
McLaren's joy was heightened by the fact Lando Norris secured second, the Briton's best result of his career, to give McLaren its first one-two in 11 years, when Hamilton beat Button to victory in 2010 Canadian GP.
McLaren can thank Hamilton and Verstappen for the long-overdue success given what unfolded between the two at the start of lap 25 of the 53-lap race.
Just two months ago on a sprint race weekend, Verstappen suffered a 150mph, 51g crash during the British Grand Prix at Silverstone after a collision with Hamilton.
On this occasion at a remarkable race at Monza, there was the stunning sight of Verstappen's Red Bull left perched on top of Hamilton's Mercedes after their latest coming together.
On this occasion, Hamilton was rejoining from the pits after opting to start on the hard tyres and run an alternate strategy to Verstappen and the McLaren duo.
Verstappen had lost time with an 11-second stop just a few laps beforehand and as Hamilton merged into the Rettifilo, the Mercedes squeezed the Red Bull at the apex of the chicane.
Neither would yield and as their tyres tangled, Verstappen hit the sausage kerb at the apex of the corner, first with the front-left tyre and then the rear.
With the latter, the Red Bull bounced up off the kerb and onto the top of Hamilton's car, with the right-rear wheel, in particular, hitting the top of the roll hoop and then the halo as Hamilton ducked low, with it seemingly brushing the top of his helmet.
Without the halo, the wheel would almost certainly have hit Hamilton hard.
The incident left both cars in the gravel and Verstappen embarking on a furious long walk back to his garage where he told advisor Dr Helmut Marko "he [Hamilton] just never gives me enough space".
Hamilton more wearily, and eventually after a long period of time, exited his car, and leaves Monza five points adrift of Verstappen in the drivers' standings.
It was their second incident of the race.
From his first front-row start since Mexico 2018, when he was on pole ahead of his then Red Bull team-mate Verstappen, Ricciardo delivered the ideal getaway.
On the long run down to the first chicane, Ricciardo managed to get his nose in front of Verstappen to lead a grand prix for the first time since the final race of 2018 in Abu Dhabi, which proved to be his last with Red Bull.
Behind him, Hamilton had performed a similar manoeuvre on the second McLaren of Lando Norris, even more remarkably given the seven-time champion had started the race on the hard tyre.
Every other driver around Hamilton, down to and including Nikita Mazepin in his Haas in 16th, had selected the medium compound.
After clearing Norris, through the Curva Grande and hurtling into the second chicane, Hamilton then pulled alongside and challenged Verstappen for second place.
But the duo touched wheels, forcing Hamilton onto the rumble strips, similar to their incident earlier in the season at Imola.
Hamilton's loss of momentum resulted in Norris being able to reclaim third place, soon after which a virtual safety car was called.
Fortunately for Sainz, he escaped damage to his SF21, but Giovinazzi lost his front wing, obviously necessitating a pit stop, and earning a five-second time penalty from the stewards for an unsafe rejoin.
Once the VSC ended, the two McLarens then became a frustration for Verstappen and Hamilton as neither of the title fighters could make an impression on the two MCL35Ms.
Hamilton did have one opportunity on lap 12 but twice had to back out of his attacks into the first two chicanes, following which there was a period of stabilisation.
As the medium tyres began to wear, in particular, Verstappen then suffered a lock-up on lap 20 into the first chicane, taking to the rumble strips.
Two laps later, McLaren blinked first by bringing in Ricciardo, giving Verstappen the chance of an undercut, only for the kings of the sub-two-second stop to falter.
The 11-second stop dropped Verstappen into the midfield, at which point Hamilton finally made his way past Norris and into the lead of the race.
At that stage, Hamilton was on course for his 100th win until it all unravelled soon after in the moments following his pit stop.
After six laps behind the safety car, the race resumed on lap 31, with Ricciardo going on to claim an astonishing triumph ahead of team-mate Norris for McLaren's first win since the final race of 2012 in Brazil.
Ricciardo also claimed the point for fastest lap to add to his tally for the day.
Sergio Perez finished third on track, but had earlier been handed a five-second time penalty for gaining a lasting advantage off the track in a tussle with Ferrari's Charles Leclerc.
That dropped the Mexican to fifth behind Mercedes' Valtteri Bottas, who had started 19th given engine penalties he was forced to take, and Ferrari's Charles Leclerc.
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