Max Verstappen extended his championship lead over Leclerc with third place ahead of the home hero, who had dominated the early stages that followed a long delay due to a rain storm soaking the Principality.
Rain began to fall just before the scheduled start time, which was pushed back initially by nine minutes before this was extended to 16 with a safety car formation lap mandated – on safety grounds per the FIA because there had been no prior running in the wet this weekend – and in that gap the deluge intensified.
The cars were sent out for two formation lapses behind the safety car, with proceedings stopped at the end of the second as the rain was falling to such an extent huge areas of standing water formed, with rivers running around the Rascasse as the field passed by , heading for the pits.
The cars remained there for nearly 50 minutes before they were sent out for a second safety car formation lap procedure, which meant all the cars had to be fitted with extreme wet tires.
After two laps behind the safety ca, racing began with a rolling start at the end of lap three.
Leclerc led the charge ahead of Sainz, Perez and Verstappen – his Ferrari squirming around as he applied full power for the first time down the pit straight, but staying in the right direction as the Monegasque led the field into Ste Devote.
They made it through unscathed but spread out, many drivers getting very sideways coming out of Casino Square as Leclerc edged to a 1.8s lead by the end of the first racing tour as the Ferrari drivers fired their tires up quicker than the chasing Red Bull duo behind.
Leclerc soon pulled clear of Sainz, the two Ferrari drivers quicker at different points of the track, with the leader regularly pulling a second clear through sector one before Sainz stole a few tenths back in the second and third segments as they worked their way down the 1m30s laptime brackets (the first racing lap was a 1m43.218s for Leclerc).
By lap 15 Leclerc led by five seconds, with the leaders discussing with their teams whether to switch to intermediates as Pierre Gasly, Stroll and Latifi had done ahead of the rolling start.
Sainz insisted on staying out and going straight to slicks was the best option for Ferrari, but his hand was forced when Perez, who had been advocating for inters, took them at the end of lap 16.
His pace was so strong on that compound that when Ferrari brought Leclerc in on lap 18, with Verstappen doing likewise and both taking inters, Perez vaulted ahead and quickly chased after Sainz.
The Spaniard led until lap 21, by which time Perez was only a few seconds behind despite having already stopped and indeed as Sainz completed a slippery out-lap, Red Bull brought Perez and Verstappen.
As they exited the pits on lap 23, Verstappen appearing to get very close to the pitlane exit line if not go over it, Perez had leapfrogged Sainz to lead, with Verstappen slotting into third just behind and Leclerc fourth.
The former dominant leader had been brought in for a second time a few seconds behind Sainz, Ferrari giving him confusing radio messages about whether or not to come in and double-stack.
Now all the leaders ran hard slicks, but this time the Red Bulls appeared to get better tire warm-up – Sainz even nearly dropping his car as he ran closely behind Perez at the end of lap 23.
Just as Perez was starting to cement the lead he had gained while Sainz was saving his sideways moment, and then defending from Verstappen and the frustrated Leclerc behind, the race was interrupted again.
Mick Schumacher had been the first driver to take hards on lap 18 and as he battled Alfa Romeo’s Zhou Guanyu, he dropped his Haas running between the two Swimming Pool chicanes.
The impact was not at massively high speed, but the angles and forces involved snapped Schumacher’s car in half and as a result of needing to repair the barrier and clear away a large amount of wreckage the red flags came out again after the incident had first been covered by a virtual and then full safety car.
After a stoppage of 20 minutes, Perez led the pack back out for another rolling start after two more tours behind the safety car – the order behind Sainz, Verstappen, Leclerc, George Russell and Lando Norris, who had lost out to his fellow Briton by taking inters for a few laps and the Mercedes stayed out on full wets for a few more laps before going straight to slicks.
At the restart on lap 33, with the Ferraris on the same set of hards they had been running before the stoppage and Perez and Verstappen switched to new mediums, Perez was unchallenged into Ste Devote.
He did lock up heavily approaching Mirabeau, but still built a lead of nearly a second as the pack returned to racing speed in the 1m23s.
A few laps later they were down to the 1m18s, with the Ferrari cars not dropping back with slow tire warm-up despite being on a harder compound.
But after they leaders exchanged fastest lapse between the four cars over the next phase of the race, DRS now switched on and the pace reaching the 1m16s, Perez began to edge clear and Leclerc, unable to stay in the 1m16s, lost contact with Verstappen in fourth.
By lap 45 Perez’s lead was 2.2s over Sainz and his main concern became catching the rear of the field to lap the backmarkers – a long snake having formed behind Fernando Alonso, who had dropped back from Norris while leading Lewis Hamilton and Esteban Ocon.
But 10 laps later, Ferrari’s hoped for Perez’s tires to grain and wear finally arrived and the leader dropped back to the 1m18s bracket, which meant Sainz quickly erased his lead and closed in to under second, with Verstappen doing likewise and Leclerc also able to reverse his earlier losses.
Ferrari urged Sainz to pressure Perez as the leaders did catch traffic – Verstappen behind not struggling as much keeping his mediums alive to the finish, which by this point was the two-hour time limit after the repeated delays.
A final 10-minute chase ensued, with Sainz initially threatening to make a move into the chicane, but got closest, and twice nearly ran into the back of Perez, at the hairpin.
But a bold move for the lead never came, with Verstappen also not attempting a risky pass on Sainz and Leclerc kept at bay in fourth as a tense stalemate played out.
Perez completed 64 laps and finished with a final margin of 1.1s, Sainz just 0.3s clear of Verstappen and the top four covered by just 2.9s.
Russell finished a lonely fifth having been steadily dropped by the leaders in the lapse after the second rolling start, with Norris pitting during the chase to the flag as he had enough of a gap behind thanks to Alonso’s slow pace, but remaining sixth for McLaren.
Alonso did lift his laptimes as the finished approached and he finished 4.0s clear of Hamilton, who had battled with Esteban Ocon ahead of the second red flag.
The pair clashed into Turn 1 at one stage, for which Ocon was given a five-second time addition that dropped him out of the points from ninth on the road behind Hamilton at the finish.
That promoted Valtteri Bottas to ninth, Sebastian Vettel to the final point in 10th (full points were awarded as over 75% of the set distance was completed) and Gasly 11th, the AlphaTauri driver rising through the field on his inters during the laps before the Sainz and Russell stayed out to go straight to slicks.
Two other cars failed to finish: Alex Albon who stopped in the pits ahead of the closing stages and Kevin Magnussen who retired due to a water pressure loss just before Schumacher’s crash.