The first practice for the Monaco Grand Prix was headed by Charles Leclerc.
Leclerc was 0.039 seconds ahead of Verstappen.
Verstappen damaged his tyres on his final run and was forced to retire, while Carlos Sainz was third and Leclerc fourth.
Lando Norris was fifth, George Russell was eighth and Lewis Hamilton was tenth.
A number of drivers ran off the track at the first corner. Along with Verstappen, Leclerc, Perez and Magnussen all had moments there.
The session was over after Verstappen braked too late into Sainte Devote on his next flying lap, and after the other drivers had passed him, Perez overtook the world champion.
Alex Albon had a very close shave when the car went sideways towards the barrier, but he was able to save the car.
The seven-time champion managed to keep his Mercedes out of the wall at Tabac.
They hoped that a new floor in Spain would fix the problem ofporpoising on the straights that plagued them through the first five races.
Pierre Gasly was an impressive sixth with a time set on the hard tyres, ahead of Daniel Ricciardo.
The Mercedes was split in ninth place by the Aston Martin of Sebastian Vettel.