Ferrari's Carlos Sainz crashed in final practice at the Monaco Grand Prix after spending much of the day competing for fastest time.
The Spaniard had just been demoted to third by his team-mate Charles Leclerc when he clipped the inside barrier at the exit of the Swimming Pool section.
Red Bull's Max Verstappen set the pace by 0.065 seconds from Leclerc.
Sainz was third ahead of Aston Martin's Fernando Alonso. Lewis Hamilton was only sixth in the upgraded Mercedes.
The former champions have introduced an upgrade to their car that features new front suspension, sidepods and floor after accepting at the start of the season that they had made a mistake by pursuing a unique design direction that has left them uncompetitive for the last two years.
Hamilton ended the session 0.498secs off the pace, and when told where he was losing out to the fastest cars said over the radio: "Damn. The car won't go much quicker than that."
Hamilton was split from the top four by an impressive performance from Lando Norris in the McLaren, fifth fastest in a car that has struggled for much of the season.
Verstappen's team-mate Sergio Perez, the Dutchman's only vaguely realistic title rival this year, was down in seventh place.
On the evidence of Friday, the weekend looks set to be a competition between Red Bull, Ferrari and Alonso, with the world champions potentially facing a tougher challenge than at most other tracks so far this year.
Sainz was the most impressive Ferrari driver for much of the day, while Leclerc was struggling to get close to the Spaniard.
But coming to the end of his series of laps on the softest tyre, Sainz misjudged his entry to the second part of the Swimming Pool and hit the inside barrier a glancing blow.
That broke his suspension and sent him into the barrier on the outside in a virtual carbon copy of the crash Leclerc suffered in qualifying last year.
Valtteri Bottas, driving an upgraded Alfa Romeo, was eighth fastest, with the Alpines of Pierre Gasly and Esteban Ocon completing the top 10.
Alex Albon, who crashed his Williams at the end of the first session earlier in the day, missed much of the second as the team repaired his car. He got out for a few laps at the end but ended up slowest of all.