The prelude to the sole practice session featured rain, and a wet track greeted the drivers as they sought to cram their sprint weekend preparation into the hour-long running.
Alex Albon was first to brave the conditions on the intermediate tyre, followed by team-mate Logan Sargeant, as Lewis Hamilton emerged on the wet tyre in his first run with Mercedes' new upgrades.
Albon set the first timed lap, a 2m08.394s, as rainfall began to slowly intensify in the early phases of the session. Hamilton's opener on wet tyres was 1.9 seconds slower than the Williams driver's time.
Although Albon looked set to improve on his first time, he was unable to slow down to successfully navigate the Bus Stop chicane and had to retreat to the pits after gathering his car out of the run-off.
Yuki Tsunoda placed his car above Hamilton's in the order by almost 0.2s, and subsequently held control of his AlphaTauri on his next visit to Eau Rouge as his car wiggled halfway up the hill to force him into driving over the Raidillon run-off.
The early running then quickly dried up as the standing water around the seven-kilometre Spa-Francorchamps grew with the worsening rain, although Carlos Sainz, Lando Norris, and Sergio Perez elected to brave the conditions on the wet tyres once the session's opening 15 minutes came to an end.
Sainz grabbed a 2m09.081s to slot in behind Albon as he continued to circulate around the circuit, while Norris joined a host of other emerging runners onto the intermediate tyre as track conditions looked to improve slightly.
Pierre Gasly had also taken to the track on the intermediate tyre and was set to beat Albon's lap, but locked up into the Bus Stop. Charles Leclerc instead took over at the top on the wet compound, setting a 2m08.148s.
Source: Autosport