Lewis Hamilton set the early pace as F1 visited Saudi Arabia for the first time.
The Mercedes driver, who trails Red Bull's Max Verstappen by eight points going into the final two races of a monumental campaign, posted a time of one minute 29.786s around the new Jeddah Corniche Circuit.
Hamilton finished narrowly ahead of Verstappen by just 0.056s, with team-mate Valtteri Bottas almost a quarter of a second adrift.
At this stage of the season, the track that is set alongside the Red Sea, is throwing an unknown element into the mix for all drivers and teams, but primarily for Verstappen and Hamilton due to their fight for the title.
Naturally, the first session was about learning the circuit, with the teams evaluating their simulation work and seeing if it tallied with live data, and then progressing from that point ahead of FP2 and the remainder of the weekend.
Coming into the weekend, there had been early concerns due to the incredibly dusty nature of the asphalt but remarkable work through the night resulted in a circuit fit for F1.
Dubbed 'the fastest street circuit in F1', the venue certainly lived up to its billing as the 27-turn, 6.1km - the second-longest track in the sport after Spa-Francorchamps - was covered in just 90 seconds by the leading players.
Verstappen was quickly on the pace, setting the initial fastest lap before continually lowering the benchmark with a number of soft-tyre runs.
At the halfway stage the Dutch driver had set a time of 1:30.014s, with Hamilton six-tenths of a second adrift, followed by Bottas, with the trio the only drivers in the one minute 30s.
Bottas then set the fastest first two sectors with around 24 minutes remaining before backing off in the final sector, underlining the available pace in the Mercedes.
While on that lap there was a moment of consternation in the Red Bull garage as his car required a thorough check following an aggressive run over the kerbs at turn 22.
Bottas eventually shaved five-thousandths of a second off of Verstappen's time which prompted a radio message of "F***, this track is cool".
It was Hamilton, though, who became the first driver to dip below the 90-second mark as he posted what proved to be the leading time of 1:29.786s.
It is known Hamilton is running the engine that propelled him to a historic win in Brazil recently, although it is fair to assume Mercedes will likely have used an older spec for Friday practice before a change going into Saturday to preserve the life of the former.
It appeared as if Hamilton would set a Mercedes one-two before Verstappen threw in a late hot lap to move within touching distance of the seven-time champion.
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