Charles Leclerc set the pace from Lando Norris in first practice at the season-ending Abu Dhabi Grand Prix - but Ferrari's Constructors' Championship title hopes have already suffered a huge blow after their driver was handed a 10-place grid penalty for Sunday's race.
Just moments after Leclerc had topped the opening session at the Yas Marina Circuit in what had appeared an early boost to their prospects, Ferrari confirmed a battery change on the Monegasque's car from the start of the session would trigger a costly 10-place grid drop for the grand prix.
Ferrari trail McLaren by 21 points heading into the 2024 F1 finale and realistically need a one-two race finish to truly place their rivals under pressure as they chase a first constructors' crown since 2008.
But Leclerc will now start no higher than 11th on Sunday's grid.
In an opening session which saw six of the grid's regular drivers - including world champion Max Verstappen - watch from the sidelines while teams completed their requirements to give practice track time during the year to rookies, Leclerc had pipped McLaren rival Norris to the quickest time late in the session with a best lap of 1:24.321.
Leclerc's fastest time came during a practice in which he made joint history with his younger brother Arthur by becoming the first siblings to be team-mates in the same session.
Arthur Leclerc, who is a development driver at the Scuderia, was 18th quickest on his P1 debut as he stood in for Carlos Sainz.
Norris finished two-tenths of a second back from the senior Leclerc with the Mercedes pair of Lewis Hamilton and George Russell third and fourth respectively.
Hamilton is competing in his final weekend as a Mercedes driver after 12 years ahead of his winter switch to Ferrari.
The seven-time world champion headed to the stewards after the opening session for allegedly impeding Norris midway through the session at the final corner. After hearing from both drivers, stewards concluded the incident was simply a "misunderstanding" and warranted no further action.
Nico Hulkenberg was sixth at the start of his Haas swansong and Franco Colapinto was seventh for Williams, but it was confirmed during the session that both the Argentine and Alex Albon will take five-place grid penalties for Sunday's race for exceeding gearbox usage limits.
Aston Martin reserve Felipe Drugovich was the fastest non-race driver in ninth. Sergio Perez took 10th for Red Bull with his future at the team beyond this weekend looking increasingly precarious.
Young drivers get chances to shine on the main stage
As has traditionally been the case since the Yas Marina Circuit joined the calendar in 2009, first practice in Abu Dhabi is regarded as one of the year's least representative sessions given it takes place in daytime conditions whereas the rest of the race weekend - Saturday's final practice aside - is staged in cooler evening conditions under floodlights.
That fact, and the event's position at the end of the calendar, also inevitably means teams use this P1 session to make sure they fulfil their requirements for running with inexperienced drivers.
Teams must give two P1 sessions per season over to drivers with fewer than three grands prix starts and Friday morning saw six teams - McLaren, Ferrari, Red Bull, Aston Martin, RB and Williams - fulfil their respected second.
While Aston Martin's Drugovich (ninth fastest), Red Bull's F2 title-chasing Isack Hadjar (15th) and RB's Japanese driver Ayumu Iwasa (17th) had appeared in practice sessions before, there were F1 Friday debuts for Ferrari's younger Leclerc (18th), McLaren's Ryo Hirakawa (14th) and Williams' British youngster Luke Browning (20th).
Hadjar, who is also battling for the F2 title this weekend against Gabriel Bortoleto with half a point separating the pair, spun early on in the session.
Jack Doohan also falls into the category of drivers with fewer than three GP starts to his name but the Australian is making his full race weekend debut for Alpine here after Esteban Ocon's early departure ahead of his Haas switch. Doohan completed 24 laps on the way to the 19th-quickest time.
Sky Sports F1's live Abu Dhabi GP schedule
Friday December 6
12.45pm: Abu Dhabi GP Practice Two (session starts at 1pm)*
2.30pm: F1 Academy Qualifying*
3.15pm: The F1 Show*
Saturday December 7
8.10am: F1 Academy Race One
10.15am: Abu Dhabi GP Practice Three (session starts at 10.30am)
12.10pm: F2 Sprint Race
1.15pm: Abu Dhabi GP Qualifying build-up
2pm: ABU DHABI GP QUALIFYING*
4pm: F1 Academy: Race Two
5pm: Ted's Qualifying Notebook
Sunday December 8
7.10am: F1 Academy Race Three
9.20am: F2 Feature Race
11.30am: Grand Prix Sunday: Abu Dhabi GP build-up
1pm: The ABU DHABI GRAND PRIX
3pm: Chequered Flag: Abu Dhabi GP reaction
4pm: Ted's Notebook
*also live on Sky Sports Main Event
Watch the final race of the 2024 Formula 1 season - the Abu Dhabi Grand Prix - live on Sky Sports F1, with Sunday's race at 1pm. Get Sky Sports F1 or stream with NOW
