Montoya maintained his start-line advantage and led until he exited a chicane slowly due to a tyre blister and was overtaken by Barrichello on the ninth lap.

Barrichello pulled away from Montoya and held the lead until his first of two pit stops on lap 19 which proved problematic because of a faulty refuelling rig that had been reprogrammed.

The result meant Montoya moved into fifth position in the World Drivers' Championship, 83 points behind leader Michael Schumacher who clinched the title two races beforehand at the Hungarian Grand Prix.

Williams' strong finish meant the gap between themselves and McLaren was reduced to eight points in the World Constructors' Championship with two races remaining in the season.

[9][11] After the September 11 attacks on New York and Washington D.C., Formula One's governing body, the Fédération Internationale de l'Automobile (FIA) announced that the Italian Grand Prix would go ahead as scheduled.

[13] Additionally, the Automobile Club d'Italia urged fans and spectators to behave "in keeping with the gravity of the situation and in collective participation in the pain of American citizens.

"[12] Podium celebrations were also cancelled and all pre-race ceremonies including a flypast by the Italian Tricolour Arrows display team were called off.

"[20] Michael Schumacher was intent to help his teammate Barrichello finish second in the World Drivers' Championship and revealed that Ferrari technical director Ross Brawn had told him "it doesn't feel much difference this race to the others", adding, "That is because we are still trying to keep winning races and that means the emotions, the pressures and the nervousness is pretty much the same, whether or not we have won the world championship.

[23]: 88, 94 Due to the configuration of the Autodromo Nazionale di Monza, with its high average speed, the teams set up their cars to produce the minimum amount of downforce possible.

[35][36] Montoya recorded the third session's fastest lap of 1:25.558 with fewer than ten minutes remaining in clear weather conditions but on a damp circuit that was created by a thunderstorm on Friday night which meant the track was slow to dry.

De La Rosa, BAR drivers Villeneuve and Panis, Räikkönen, Irvine, Verstappen, Enrique Bernoldi for Arrows and Heidfeld rounded out the top ten.

Benetton's Giancarlo Fisichella, Yoong, Button, Alesi, Michael Schumacher, Coulthard, Häkkinen and Minardi's Fernando Alonso set no laps during the session.

[6] The session was held in dry weather conditions,[30] and rises in air and track temperature gave Michelin-shod teams a speed advantage.

[42] Häkkinen took seventh and ran wide on the kerb at the exit of Curva di Lesmo on his final timed run and heavily damaged his car against the outside barrier with four minutes to go.

[30][41][42] The drivers participated in a 30-minute warm-up session for teams to adjust their cars and setups and experiment with different levels of fuel before determining their strategies at 09:30 local time.

[48] After the end of the warm-up but before the race at 11:15 local time, a second minute of silence was organised by the Italian National Olympic Committee prior to the beginning of the Drivers' Parade.

[57][58] Further back, Trulli was hit by Button, who drove too fast on the slippery outside line going into the chicane, braked too late, and was sent into a spin and became the first retirement of the race.

[52] Irvine moved from 13th to seventh by the end of the first lap, as Häkkinen went through the chicane to avoid making contact with other drivers and fell to thirteenth.

Coulthard became the third retirement of the Grand Prix after an engine failure on lap seven, which meant Verstappen inherited fifth and Räikkönen moved into sixth.

[56] Montoya had a blister on one of his rear tyres which caused him to slide under braking,[61] and was slow exiting the Variante della Roggia chicane because he out-braked himself into the turn, which allowed Barrichello to take the lead on the entry to the second Lesmo corner on the ninth lap.

[57] Michael Schumacher battled for Montoya for third until he became the first of the leading drivers to make a scheduled pit stop on lap 18, and rejoined the track in fourth.

[62][65] Barrichello (on a lighter fuel load) was able to quickly extend his lead over Montoya to ten seconds by his first pit stop on lap 19.

[60] Schumacher out-braked himself and drove onto the concrete run-off on the inside of the left-hand part of the Variante Goodyear chicane after attempting to defend his position.

He allowed Barrichello past on the inside into the Curva Grande for second because Schumacher was aware that the race stewards would impose a stop-and-go penalty on him for cutting the first chicane.

[30][62] Yoong retired from the event on the following lap after spinning his car into the gravel trap at the first Lesmo corner,[58][2] and yellow flags were waved.

[71] Barrichello said that he felt that Ferrari put on "a good show" despite his slow pit stop from a fuel rig problem on lap 19.

[71] When asked if his car was inconsistent during the Grand Prix, Ralf Schumacher said this was not the case and stated although he had problem with his tyres he felt the Williams finish of first and third was "a great achievement".

"[72] FIA president Max Mosley stated that he disagreed with the pact and said that the drivers should have raised the concerns in the months leading up to the Grand Prix.

[73] Brawn insisted the reason Ferrari opted for a two-stop strategy was to defeat Williams tactically on the high-speed circuit, adding: "We'd been trounced at Hockenheim, and I didn't really see the point in following a couple of ultra-quick BMWs down the straight.

"[74] Jean Todt, Ferrari team principal, admitted that the refuelling rig issue at Barrichello's first pit stop possibly lost the driver the opportunity to win the race.