Ferrari's Charles Leclerc had just led away easily from pole ahead of McLaren driver Oscar Piastri, while behind Carlos Sainz first attacked Piastri at Ste Devote and then slid off at Casino Square with a suspected puncture.
Perez was eliminated by Kevin Magnussen trying to poke his nose into a gap on the run up the hill before Massenet, with their crash wreckage then swinging across the track and taking out Nico Hulkenberg as he tried to come by from just behind.
All three smashed cars continued sliding across the track and into the barriers at Massenet, with debris and wreckage strewn across the track.
Before he climbed out of his crashed SF-24, Hulkenberg witheringly called the incident "unnecessary".
The stewards have decreed that the crash does not merit further investigation and so although Magnussen is already on the verge a race ban with 10 penalty points on his superlicence, he will not face an automatic ban for the next race in Canada.
There was also a third incident on the opening lap just before the red flag was declared as the leaders traversed the Nouvelle chicane, with the Alpine drivers clashing on the exit of Portier as they headed towards the tunnel.
Esteban Ocon had just dived down Pierre Gasly's inside of the right-hander when they tangled on the exit and Ocon's Alpine was launched into the air before slamming back down onto the road and continuing on as the pack returned to the pits to wait out the clear up from the various incidents.
Sainz was able to recover the pits after waiting for the rest of the pack to plunge by at Casino Square.
After his Ste Devote attack, the Spaniard made light contact with Piastri's right rear and appeared to already be suffering from a problem when he locked up at Massenet and then went straight on as he braked for the right-hander in Casio Square seconds later.
This allowed Lando Norris to move up to third ahead of George Russell and Max Verstappen – the lead cars starting on the hard tyres with the four lead cars on the grid fitted with mediums.
Under the red flag, Leclerc, Piastri and Norris are allowed by the rules to change to the hard tyres and then attempt to run to the finish without stopping.
Sainz will take the standing restart at 3.44pm local time back in place, as the FIA has ruled that not all cars had passed the first sector line, with Sauber's Zhou Guanyu held up by the Perez/Haas crash and still on his way down to the end of the lap's opening third when the red flag was thrown.
