A dirty track surface left drivers searching for grip at the start of Friday's practice programme as conditions posed an early challenge at the Autódromo Hermanos Rodríguez.
The start to FP1 was disrupted when spins at Turn 16 for Ferraris Charles Leclerc and Red Bull's Sergio Perez led to a brief Virtual Safety Car period.
When green flag running resumed, Lance and Sebastian established a baseline for the AMR21 by running differing programmes.
With Lance set to start near the back of the field due to power unit-related penalties, his programme largely focused on longer runs and race preparations.
Mexican Grand Prix
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After delivering a 1.22.233 benchmark, Lance ran solely on the Soft tyres and refined his lap time to conclude his first run with a 1.20.945 lap time, briefly placing inside the top 10.
Sebastian, meanwhile, continually improved on the Hard tyres, producing a 1.21.584 lap before switching to a set of new Softs at the halfway point.
A 1.19.858 run with 20 minutes remaining marked the German's best lap in the morning session, finishing 10th after 27 laps.
Lance was only a handful of tenths shy of his team-mate, with his 1.20.030 lap from his second stint placing the Canadian in 13th, also with 27 laps on the board.
In FP2, Lance alternated between the Medium and Hard tyres to deliver a 1.19.730 run while evaluating the mid-range compound.
Sebastian started the session by preparing for qualifying, and bettered an early 1.19.838 on the Mediums with a 1.18.681 lap on new Softs.
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In the second half of the session, Sebastian joined Lance in race preparations, with the pair turning a combined 68 laps in FP2 and a total of 122 laps on Friday.
Sebastian was ninth at the close of FP2 to rank inside the top 10 in both Friday practice sessions while Lance ended the day's proceedings in 17th.
Sebastian: "It was a decent start to the weekend and it was good fun, despite the dusty and slippery conditions. I felt happy in the car and we gradually worked through the programme and built up the knowledge of the tyres.
"It is difficult to know exactly where we stand because the track was constantly evolving and getting quicker and quicker throughout the day. I think we have made good progress, though, and I expect it to be very close in and around the top 10.
"As ever, we will aim to fight for Q3, but I think all the teams have more to extract, as do we. Let's see tomorrow."
Lance: "As we are expecting to start towards the back of the grid due to power unit change penalties, the focus today was on the longer runs and race pace, so it was a different programme to usual.
"I think we have made some encouraging progress, but tonight we will go away and look into ways to improve the car. It was dusty on track early on, so FP3 tomorrow will be a useful session to learn more about the car.
"The goal is to make sure we are in a good place to fight our way through the field on Sunday."
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