Carlos Sainz and Charles Leclerc headed the opening practice session at the Formula 1 Mexico Grand Prix which was twice interrupted by red flags.
The Ferrari pair moved to the top during the Qualifying simulation phase of the 60-minute outing to head Sergio Perez and Max Verstappen.
However, the session ended four minutes early due to a red flag for Liam Lawson, the second time the red flag had been shown.
A total of five substitute drivers were in action as part of team’s need to run a young driver during two Free Practice 1 sessions this season.
Lawson had stepped into the Scuderia AlphaTauri of Yuki Tsunoda, while Logan Sargeant, Nyck de Vries, Pietro Fittipaldi, and Jack Doohan were also in action.
Doohan was the only of that quintet to be making his maiden Formula 1 race weekend appearance.
The Australian was in action in place of Esteban Ocon for Alpine and headed out immediately as the session began.
Lawson quickly complained of braking issues aboard the Scuderia AlphaTauri and he cycled back to the pits with two laps, and no lap time, on the board.
Max Verstappen was fast out of the gate, logging a 1:22.779s to move 1.1s quicker than team-mate Sergio Perez after eight minutes.
Those times were set on the hard compound tyres, the field unanimous in its choice of the white-walled rubber.
Perez improved with nine minutes run to clock a 1:22.702s, 0.077s quicker than his team-mate who promptly went even faster.
That resulted in a 1:22.291s to move the Dutchman some 0.4s clear once more.
Approaching the mid-point of the session, Daniel Ricciardo was out of the car after complaining of brake knock in his McLaren.
Valtteri Bottas was the first to switch to soft compound tyres to sit fourth.
That became fifth when Leclerc completed a Qualifying simulation run, managing a 1:21.546s to sit 0.745s clear at the top of the standings.
The rest of the field promptly followed in switching to the softer tyres, Lando Norris rising to second with a 1:21.120s.
Ferrari saw both its drivers top the standings with Sainz on a 1:20.707s to narrowly edge Leclerc’s 1:20.753s.
Conditions on track were difficult, with little grip available to drivers.
That caught Verstappen out, the world champion-elect losing control as he navigated his way through the Esses.
On a set of soft compound tyres, he managed to keep the car out of the fence before resuming.
A problem for Guanyu Zhou saw the Alfa Romeo Sauber driver stuck at pit exit, switching the car off to stop it from overheating.
He was eventually pushed back into the lane as Pietro Fittipaldi stopped on track at Turn 2 to draw the session’s first red flag.
The team confirmed a power unit issue for the Brazilian, a fact which seems to consign Kevin Magnussen to a grid penalty with a new Ferrari engine required.
The red flag lasted for six minutes before it resumed, a mixture of tyre compounds in use as focus switched once more to race runs.
Power unit concerns at Alpine saw the squad park Doohan with 13 laps completed.
The Australian sat 19th fastest of the 20 runners, faster only than Fittipaldi.
He ultimately missed comparatively little as Lawson stopped on track in the Stadium section with an apparent power unit issue.
It drew the second red flag of the session, the Scuderia AlphaTauri’s brakes briefly catching fire before being extinguished by marshals.
With just four minutes left as officials halted running, they elected not to restart it.
That left Sainz fastest from Leclerc, with Perez third from Verstappen – the two Red Bull drivers logging identical times.
Lawson was the fastest of the five rookies, heading Sargeant, de Vries, Doohan, and Fittipaldi.
Second practice is dedicated to Pirelli tyre testing, with 90 minutes of running.
However, those who did not take part in Free Practice 1 will be afforded 45 minutes to complete the programmes they missed earlier.
Free Practice 2 begins at 16:00 local time (22:00 BST/17:00 ET/08:00 AEDT).
Results: Formula 1 Mexico City Grand Prix, Free Practice 1
Pos | Num | Driver | Team | Laps | Time |
1 | 55 | Carlos Sainz | Scuderia Ferrari | 25 | 1:20.707 |
2 | 16 | Charles Leclerc | Scuderia Ferrari | 20 | 1:20.753 |
3 | 11 | Sergio Perez | Red Bull Racing | 22 | 1:20.827 |
4 | 1 | Max Verstappen | Red Bull Racing | 22 | 1:20.827 |
5 | 44 | Lewis Hamilton | Mercedes-AMG F1 Team | 17 | 1:20.849 |
6 | 14 | Fernando Alonso | Alpine F1 Team | 26 | 1:20.899 |
7 | 77 | Valtteri Bottas | Alfa Romeo F1 Team | 23 | 1:21.083 |
8 | 4 | Lando Norris | McLaren F1 Team | 21 | 1:21.120 |
9 | 10 | Pierre Gasly | Scuderia AlphaTauri | 25 | 1:21.310 |
10 | 5 | Sebastian Vettel | Aston Martin F1 Team | 24 | 1:21.525 |
11 | 3 | Daniel Ricciardo | McLaren F1 Team | 16 | 1:21.762 |
12 | 24 | Zhou Guanyu | Alfa Romeo F1 Team | 20 | 1:21.820 |
13 | 18 | Lance Stroll | Aston Martin F1 Team | 24 | 1:21.865 |
14 | 47 | Mick Schumacher | Haas F1 Team | 22 | 1:21.952 |
15 | 6 | Nicholas Latifi | Williams Racing | 20 | 1:22.912 |
16 | 40 | Liam Lawson | Scuderia AlphaTauri | 19 | 1:23.861 |
17 | 45 | Logan Sargeant | Williams Racing | 22 | 1:24.246 |
18 | 19 | Nyck de Vries | Mercedes-AMG F1 Team | 20 | 1:24.582 |
19 | 82 | Jack Doohan | Alpine F1 Team | 13 | 1:24.615 |
20 | 51 | Pietro Fittipaldi | Haas F1 Team | 9 | 1:26.766 |