Valtteri Bottas finished fastest in a chaotic first practice for the Emilia-Romagna Grand Prix after Sergio Perez and Esteban Ocon crashed out.
Following technical trouble in Imola, television replays of the accident were not available, but Perez spun out with a left-rear puncture, while Ocon, who was following the Red Bull, stopped on track with damage to the front-right of his Alpine.
Speaking on Sky Sports, Red Bull team principal Christian Horner said the pair collided through turns five and six.
He said: "I've only had it from the driver's perspective, but it sounds like Ocon was on a slow lap, Sergio was on a flying lap, and there's been contact between the two guys."
RED FLAG 🔴 The session is halted as Sergio Perez has a problem with his rear left wheel – and Esteban Ocon suffers collateral damage 👀 Both are out of their cars and their FP1 is over #ImolaGP 🇮🇹 #F1 pic.twitter.com/aZKrVqdAGm — Formula 1 (@F1) April 16, 2021
The session was halted for almost 10 minutes while the respective cars were towed back to the garage.
Once the running resumed, it was Bottas who headed Mercedes team-mate Lewis Hamilton by just 0.041 seconds, with Red Bull's Max Verstappen third for Red Bull, 0.058 sec off the pace.
There was further drama in the concluding moments when a second red flag was issued after Nikita Mazepin lost control of his Haas through the final corner.
The Russian rookie, who crashed out on his debut in Bahrain, ran wide into the gravel before hitting the wall and breaking his front wing.
🏁 TOP TEN: FP1 🏁 BOT 📸HAMVERLECGASSAIALOSTRLATRIC#ImolaGP 🇮🇹 #F1 pic.twitter.com/AAAD8wIHbR — Formula 1 (@F1) April 16, 2021
Verstappen topped all three practice sessions at the opening round three weeks ago, so Mercedes will be pleased to see their two drivers at the top of the timings.
But the top three were covered by less than one tenth to suggest another close race following the thrills and spills of last month's curtain raiser where Hamilton held off Verstappen to open his bid for an eighth world title with a 96th career win.
Ferrari driver Charles Leclerc finished fourth on Friday morning, two tenths off Bottas, while AlphaTauri's Pierre Gasly was fifth.
Williams' George Russell finished an encouraging 11th while his British compatriot Lando Norris was 13th for McLaren.
