The two sessions were made more challenging due to ever-changing conditions and both practices started on a track surface that was damp in places.
Sebastian and Lance began the day in cool conditions on Intermediate tyres as the Formula One field sought to create a clear racing line.
After 15 minutes of running, the track was dry enough to facilitate a switch to Mediums so Sebastian and Lance could set the AMR21's baseline.
Sebastian was one of the first drivers to set a representative lap time, and moved to the top following a 1.49.324 lap time, while Lance put together a series of quick laps to move third with a 1.49.618 effort.
Belgian Grand Prix
Get ready for this weekend's Belgian Grand Prix with our in-depth preview. Hear from Lance and Sebastian, and discover the key talking points for the race ahead
Both drivers found further gains during the stint and ended the first half of the session inside the top five after Lance lapped in 1.47.569 and Sebastian toured in 1.47.657.
The final 20 minutes was largely dedicated to running on the Soft tyre, making the most of the now fully dry track.
Sebastian secured seventh after lapping in 1.46.177, while Lance posted 1.46.649 before ending the session with a short stint on a set of used Medium tyres.
Between FP1 and FP2, the rain returned, creating the classic Spa conditions - completely dry at some corners and wet at others.
Sebastian was one of a few drivers to head out immediately on the Intermediate tyres in FP2, completing two laps before returning to the pitlane.
Lance then joined his team-mate in using the Hard compound for the first time this weekend, furthering the team’s understanding of the Pirelli compounds.
A well-timed switch to Soft tyres allowed both drivers to complete flying laps before the second half of the session was disrupted.
Lance set his personal best time of 1.45.180 to secure sixth, while Sebastian finished eighth following a 1.45.336 effort.
Crashes for Charles Leclerc and Max Verstappen interrupted the final stages of the practice programme, but Aston Martin Cognizant Formula One™ Team completed a total of 68 laps on Friday.
Weather conditions are expected to worsen over the weekend, so the team will be aiming to maximise FP3 ahead of qualifying tomorrow afternoon.
Lance: "It is great to be back at Spa. I love coming here because it is such a special track. We got through our programme today to complete a good number of laps and I was comfortable in the car.
"It has been a strong start for us, but the damp conditions out there show it could be quite unpredictable on Saturday and Sunday.
"The weather being a bit of an unknown is challenging, but that makes it more exciting for us drivers. I am looking forward to getting back in the car tomorrow and building on today’s work."
Sebastian: "It is good to be back after the break and I felt comfortable in the car straight away.
"It was not easy to complete a lot of laps because of the conditions and the two red flags this afternoon, but we were able to collect some important data.
"I think there is more to come from me and the car, and we know what to work on overnight to be ready for qualifying.
"I think the changeable weather is here to stay, so reading the conditions and being on the right tyre at the right time will be key.
"Wet weather can always mix up the grid a bit, so hopefully we can capitalise on any opportunities this weekend."
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