The Monza circuit will host the penultimate round of the world championship and the great showdown on home turf of the great Italian constructors, Alfa Romeo and Ferrari. In recent years Alfa Romeo dominated grand prix racing, however over the course of 1951, the Ferrari's ran by the former Alfa Romeo racing leader, Enzo Ferrari, are quickly challenging Alfa Romeo's as the top grand prix racing team. Nonetheless, the recent non-championship race, the Bari Grand Prix, sees the Alfa Romeo championship leader, Juan Manuel Fangio, winning after a double-win streak in the championship for Ferrari in Britain and Germany. Alfa Romeo lines up four drivers for their home event. Fangio looks set to take his first title for the team whilst the reigning champion, Giuseppe Farina, has still a faint hope of reclaiming his title distanced after an unreliable season. Felice Bonetto and Consalvo Sanesi are called in to occupy the third and fourth Alfa Romeo cars. There are rumors that the team's designer, Gioacchino Colombo, is developing a Tipo 160 model to replace the 159 ahead of 1952 to stay ahead in the development race. In their efforts to beat Alfa Romeo on home turf, Ferrari prepares more cars for both their works and privateer drivers than they have ever done before. For the first time, Ferrari makes the majority of the field with the team having seven cars in Monza. Ferrari arrives with its usual four man line-up of Ascari, Luigi Villoresi, José Froilán González and Piero Taruffi. The team plans also to enter young Gianni Marzotto, a Ferrari driver from their sportscar program, however the team withdraws his entry. Peter Whitehead, Ferrari's regular privateer, is back competing in his old 125 model. Rudolf Fischer is back entering his Ferrari 212 sports car whilst Chico Landi, Brazil's best driver, plans his first grand prix entry to start in a new privately owned 375 Ferrari model.
Nonetheless for Monza, the Alfa Romeo drivers will receive the all-new updated 159M chassis, a move they hope will end the threats to their authority. B.R.M. manages to save their public face after their points finish at Silverstone, the team suffering disastrously slow development of their P15 challenger. Nonetheless, the British constructor will make their second world championship appearance at Monza. Reg Parnell, who powered B.R.M. to points on their race debut, is again representing the squad alongside the team's test driver, Ken Richardson. Simca-Gordini is becoming the leading French constructor in grand prix racing. The team as usual brought its standard line-up of Robert Manzon, Maurice Trintignant and André Simon. The team is now consistently starting to break into the top ten finishers in the field, providing its cars actually make it to the finish. The OSCA constructor will at long last make its debut at Monza. Following their departure from the Maserati factory in 1947, the surviving Maserati brothers of Bindo, Ettore and Ernesto founded the OSCA company as a rival to Maserati. At the end of 1950, the team employed many of the now disbanded Maserati team personnel for their OSCA Formula 1 venture of 1951. The team employs Prince Bira of Siam and Franco Rol, both former Maserati drivers to spearhead the project. Despite a victory for an OSCA-engined Maserati driven by Bira earlier in the season at the Goodwood Trophy, the project is having little success. It is surprising to see Bira resign from the project, similarly to the way he did with the BRM project earlier in the year on the verge of the team's debut. Franco Rol, participating in his first grand prix of the season, will be the lone driver representing the OSCA squad on their debut. Notably there is not a single Maserati taking the start of the Italian Grand Prix, the remaining cars consisting of the private Talbot-Lago entries.
Louis Rosier and Louis Chiron represent Ecurie Rosier, whilst Claes, Levegh, Giraud-Cabantous and Swaters are the final representatives of the Talbot-Lago marque. The new Alfa Romeo 159M is working exceptionally well, the Alfa Romeo's are back on top following qualifying. Fangio takes another pole position, eight tenths faster than teammate Farina's best time in second place. Ascari, the fastest Ferrari, is frustrated to be two seconds off the pace to Fangio's best practice lap time. The team's third car of Sanesi, notably has a major mishap in a practice pit-stop. Sanesi is burned when fuel is spilled over him during the stop. The incident rules Sanesi out of the race due to the significance of the burns he received in practice. Sanesi, uncomfortable with the dangers of racing cars, immediately announces his retirement. For Saturday practice, Alfa Romeo appeals to Emmanuel de Graffenried who drove previously for the team in Bremgarten. De Graffenried takes Sanesi's car for the remainder of the weekend in which he puts his Alfa Romeo seventh on the grid, one place behind teammate Bonetto. Ferrari seems to be losing out to the qualifying pace of the Alfa Romeo's. Their lead driver, Ascari, who sits third on the grid, is still a second off the best time set by polesitter Fangio. Behind Ascari on the grid, the remaining works Ferraris of González, Villoresi and Taruffi are fourth, fifth and sixth. Reg Parnell is doing an excellent job to split the slowest Alfa Romeo's to put his B.R.M. eighth on the grid. Richardson in the second B.R.M. is also doing well in tenth position. Richardson, primarily a test driver and rarely a racer, performs well in his first grand prix qualifying. However, the race officials soon discover that Richardson did not acquire the proper racing license to race in Formula 1 and is thereafter excluded from the grand prix. Raymond Mays threatens to withdraw his team from the race if Richardson is not reinstated, however it is to no avail. After failing to acquire the services of Leslie Johnson, the team then appeals to the semi-retired Hans Stuck, a successful 1930's Auto Union driver to take over the second car.
Stuck, who originally is attending the race as a spectator and has not raced in grand prix since 1939, accepts the challenge. Behind the B.R.M.'s are the little Simca-Gordini cars. The team throughout the course of the season establishes themselves ahead of Talbot-Lago; Simon, Trintignant and Manzon are eleventh, twelfth and thirteenth. Giraud-Cabantous and Rosier are the quickest Talbot-Lago cars. Chico Landi is a disappointment, he can only manage sixteenth despite driving a Ferrari 375. Chiron is seventeenth ahead of former teammate, Franco Rol, who can only manage eighteenth on the grid with the new OSCA 4500G. Whitehead's Ferrari 125 is beginning to show its age with the Brit only managing nineteenth. Levegh, Claes and Swaters are the final cars to round out the grid. Prior to the start of the race, B.R.M. is encountering more problems. Both the cars of their stand-in driver, Hans Stuck, and their lead driver, Reg Parnell, develop gearbox problems in the morning before the race. It is an ironic turn of events: due to gearbox problems, the B.R.M. team will be forced to withdraw both its entries from the race. Only a day earlier, team manager Raymond Mays was threatening to withdraw both his cars following the denial of Richardson's race entry. Despite a good showing in qualifying, the B.R.M.'s will once again be hampered by their poor reliability. The crowd instead turns its attention to the battle for dominance among the Italian giants, Alfa Romeo and Ferrari on home turf. The start sees Alfa Romeo take the early advantage, Fangio getting a clean get-away ahead of Farina's second Alfa Romeo. Ascari's Ferrari does not make the best of starts, dropping behind teammate González going into the first corner. However, it is immediately evident that Ascari has pace. By the end of the third lap, Ascari takes the lead after steadily progressing past González, Farina and Fangio ahead of him. Chico Landi in the private Ferrari 375 has an unsuccessful debut, his car failing to complete a single lap.
A lap later, Whitehead's old 125 Ferrari and the fourth Alfa Romeo of De Graffenried also retire. Claes is also an early retirement on lap four with an oil pump failure. On lap five, Farina begins to drop back due to an engine misfire. After dropping to last place, Farina decides to come into the pits for repairs on lap eight. However the mechanics find a terminal oil system problem, forcing the world champion out of the race. Ascari is left leading whilst Fangio, once again being surrounded by the Ferraris, gives chase in second place. He retakes the lead, however on lap 13 he develops a puncture which forces him to drop behind Ascari, González, Villoresi and Bonetto. Fangio pulls into the pits for new tyres as does Taruffi's Ferrari. Taruffi is also unfortunate to receive a puncture at the same time as Fangio, the Ferrari's tyre disintegrates to the point there is barely any rubber left on the wheel rim when he returns to the pits. Fangio rejoins the race in fifth place, but quickly becomes fourth as Villoresi also begins to encounter tyre troubles and heads for the pits. Fangio, pushing hard, makes his way past Bonetto's Alfa Romeo, now being able to give chase to the leading Ferrari's of Ascari and González, who now opens a big lead in the race. The high-speed circuit continues to dwindle the field, cars continually drop out with mechanical trouble. The Talbot-Lago's of Claes, Swaters, Levegh and Chiron are all out of the race before the tenth lap. Manzon and Trintignant's Simca-Gordini retire at the same time on lap 29 with engine troubles. Fangio is brought into the pits for a fuel stop on lap 27, his progress on retaking the lead being temporarily halted. Two laps later, Bonetto is also into the pits for fuel. Bonetto exits the car to allow Farina, one of the lead drivers, to rejoin the race. Farina rejoins the race in fourth place, behind Fangio and the Ferrari's of Ascari and González. Villoresi meanwhile is unlucky and sustains a second puncture, forcing him into the pits for a second time. A few laps after the Alfa Romeo’s, the lead Ferrari's of Ascari and González make their pit-stops.
Luckily for them, their stops go without drama and they rejoin the track ahead of Fangio who is chasing once again. However Fangio's chase is halted when he begins to suffer an engine misfire. On lap 39, the misfire becomes terminal and the lead Alfa Romeo is forced to retire. This means that Farina, who is driving Bonetto's car, becomes Alfa Romeo's last hope in the race. On lap 40, Farina is 40 seconds behind González in second place. However after only fifteen laps, Farina, after a frantic chase, closes to within seven seconds of González. Farina is then hampered during his second pit-stop when a wheel fails to attach correctly. However despite this mishap, Farina goes out of the pits and continues to give chase to González and Ascari ahead of him. However on lap 70, only ten laps from the end, Farina's car unexpectedly suffers an engine cut whilst exiting the Parabolica. He coasts into the pits where the mechanics quickly discover a cracked fuel tank. The mechanics fill his car's fuel tank, hoping the car will not lose that much fuel to make it to the finish. Farina returns to the track, however his brilliant chase on the Ferrari’s is brought to an end. Ascari meanwhile is cruising out front, by the finish he extends the gap to González by 24.6 seconds, taking a comfortable second victory of the season. Ferrari will therefore prove triumphant on home turf, Alfa Romeo is defeated, only the share car of Farina and Bonetto manages to limp home in third place. The final Ferrari's of Villoresi and Taruffi round out the points following their own race troubles. Simon brings his Simca-Gordini home in sixth, the little Simca-Gordini squad defeats once again their established Talbot-Lago rivals. Rosier and Giraud-Cabantous are the sole Talbot-Lago's to make it to the finish in seventh and eighth place. The final classified finisher is the OSCA of Franco Rol. Rol completes the OSCA's first race, 13 laps down to the leaders. It was an unsuccessful debut for the team's Formula 1 project which encountered troubles all year.