Charles Leclerc set the pace from team-mate Lewis Hamilton in first practice as Ferrari strengthened their status as favourites for the Monaco Grand Prix weekend, with championship leaders Mercedes only fourth and fifth.
In the opening session around Formula 1's most-famous circuit on one of the sport's showpiece weekends, Ferrari's drivers were straight in a groove on a twisty track that had been tipped by rivals to particularly suit their 2026 car.
Monaco's own Leclerc - who earlier this week renewed his contract at the team - topped the session by 0.226s from Hamilton with a best lap of 1:13.978. Max Verstappen took third for Red Bull but he alone was half a second off the pace.
Mercedes have claimed every Grand Prix pole and race win so far this season but the feeling is that they will have their work cut out to extend those runs this weekend.
Championship leader Kimi Antonelli was the quicker of the Mercedes drivers throughout the session and while he finished within a tenth of Verstappen in fourth, team-mate George Russell was a further half a second behind in fifth.
McLaren won last year's Monaco race with Lando Norris but finished the first session over one second behind Ferrari this time, with the reigning world champion sixth and Oscar Piastri eighth.
On Ferrari's fast start, Your Site F1's Martin Brundle said: "It looked good, didn't it?
"Charles had a couple of adventures early on, the lock-up [at Mirabeau] on the out-lap and he went across the chicane, while they were still struggling with understeer. But the raw pace looked extremely good."
Audi enjoyed a positive start to the weekend with Nico Hulkenberg seventh and Gabriel Bortoleto ninth, while Alpine's Pierre Gasly rounded out the top 10.
Two drivers crashed during the opening hour of running around the barrier-lined track.
Isack Hadjar's incident was the most significant when he lost control of his Red Bull exiting the higher-speed Swimming Pool section. The rear of his car got away from him through the sharp right-hander and sent him towards the outside wall and out of the session with 25 minutes to go, much to the Frenchman's surprise.
"Yeah [I'm fine], but I don't understand why it snapped off like that," said Hadjar on Red Bull team radio. "I'm sorry."
Norris had avoided a similar incident minutes before when he successfully corrected a slide out of the corner, the McLaren driver instead clattering over the kerbs and avoiding the barriers.
Two-time Monaco winner Fernando Alonso broke his Aston Martin's front wing against the barriers when his car snapped left under braking coming out of the tunnel into the harbourside chicane. The Spaniard was at least able to continue and return his damaged car to the pits.
Both incidents caused brief red flags in a session that saw numerous drivers find the run-off areas, including pacesetter Leclerc twice and Hamilton once.
Friday June 5
2.05pm: F2 Qualifying
3pm: Team Bosses' Press Conference
3.30pm: Monaco GP Practice Two (session starts at 4pm)
5.15pm: The F1 Show
Saturday June 6
9.40am: F3 Sprint
11.15am: Monaco GP Practice Three (session starts at 11.30am)
1.10pm: F2 Sprint
2.15pm: Monaco GP Qualifying build-up
3pm: MONACO GP QUALIFYING*
Sunday June 7
6.50am: F3 Feature Race
8.30am: F2 Feature Race
10.50am: Porsche Supercup
12.30pm: Monaco GP build-up: Grand Prix Sunday*
2pm: THE MONACO GRAND PRIX*
4pm: Monaco GP reaction: Chequered Flag*
*Also on Your Site Main Event
Watch the Monaco Grand Prix, the first of six races in eight weeks, live on Your Site F1 this weekend.
