Lance finished in the top five in both Free Practice sessions as track action resumed at Spa-Francorchamps after the summer break.
Both sessions were run in mixed conditions, and Lance featured strongly in the AMR22 across the day.
Sebastian, meanwhile, had his running interrupted by a poorly timed red flag.
Lance
Lance started FP1 with an installation lap on Intermediate tyres, but it quickly became apparent that the circuit was dry enough for slicks.
He then ran on the Hard compound, putting in a best lap of 1.50.277 during a seven-lap run.
Lance then switched to the Soft-compound tyre and posted a 1.47.437 before a red-flag stoppage, this left him fifth-fastest overall.
Belgian GP
A series of sweeping high-speed corners, mighty elevation changes and highly unpredictable weather conditions all make Spa one of the most challenging and fearsome circuits in the world.
The stoppage was fairly lengthy, and the conditions had worsened by the time the session resumed with 10 minutes remaining.
Lance completed another couple of laps on his Soft tyres, before the rain set in and effectively ended the session early.
The rain had eased by the start of FP2, and Lance got in his first Medium-tyre running of the weekend.
During his seven-lap run, he put in a best time of 1.48.912, before switching to a new set of Soft tyres.
On those, he put in a 1.46.635 to go fourth fastest, before switching back to the Medium tyres from earlier just before the rain returned, completing 16 laps in total in the session.
"It felt good out there today and the lap-times looked good as well. We tried all the tyre compounds, and the performance felt decent across all three.
"We do not know what the weather will bring tomorrow, so it is really tricky to figure out where we will be when qualifying comes around, but I am hopeful we will be in the mix for some good points this weekend."
Sebastian
With some dampness still in the air at the start of FP1, Sebastian started his session with an installation lap on the Intermediate tyre.
He then switched to the Medium compound when it became clear that the track was dry, and posted a time of 1.49.813 during his six-lap run.
For the next part of the session, Sebastian switched to the Soft tyre, but he was just about to start a flying lap when a stopped car brought out a lengthy interruption to the session.
When the session resumed, the rain started to fall and Sebastian was able to set a representative Soft tyre time, leaving him 15th overall with 12 laps completed.
Sebastian started FP2 on the Hard compound tyre and posted a 1.50.329 on those tyres during a nine-lap run, before a switch to the Soft tyres.
His best effort was a 1.47.867 before the rain arrived again. A light shower allowed Sebastian to return to the track at the end on his used Soft tyres for a practice start.
"It is always great to drive at Spa – even in today's changeable conditions. I struggled a little bit in the second session – I did not really feel very confident with the car – but I am pretty sure tomorrow will be better.
"The sessions were mostly dry, but it was more about trying to find a feel with the car today. We will have a proper look at the data tonight and I am sure we will take a step forward for tomorrow."
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