Seven months after the 2019 campaign concluded, the coronavirus-delayed new season began under cloudy skies at the Red Bull Ring, with little action taking place in the first third of the 90-minute session.
Most cars were kept in their garages after the field completed the initial installation laps, although the McLaren drivers Carlos Sainz and Lando Norris, along with Bottas, set the early pace.
But the trio joined the rest in the pits after 20 minutes as a wet track was declared following a light smattering of rain.
Ferrari's Sebastian Vettel led the field back out for a few laps on the intermediates, but the drivers quickly concluded that the track was not wet enough to use the grooved rubber.
Shortly after the session's first third had been completed, Hamilton set his first flying laps on the hard Pirelli rubber, improving on three successive laps to soon claim the top spot with a 1m06.994s.
Racing Point's Sergio Perez looked set to depose Hamilton soon afterwards but his RP20 began smoking around his flying lap and he had to abandon his effort so the issue could be rectified.
Hamilton continued to improve the best time, briefly interrupted by Lance Stroll before the Racing Point driver had his time deleted for a track limits infringement at the exit of the penultimate corner.
A flurry of action in the middle of the session led to Sainz, Stroll and Renault's Daniel Ricciardo enjoying brief spells in first place, with Perez then taking the top spot as soon as he returned to the track to head a brief Racing Point 1-2 with 1m06.052s.
But as the session approached the one-hour mark, the Mercedes cars returned to the fray after a chunk of time waiting in their garages, with Bottas bettering Perez's improved best of 1m05.773s to a 1m05.486s on the softs.
Hamilton then used his own first effort on the red-walled soft tyres to retake first with a 1m04.968s – attacking the kerbs at the exit for the Turn 7/8 fast chicane and the final with apparent gusto.
The world champion then improved the fastest time to a 1m04.816s with 27 minutes remaining, which stood as the session's until the end – Bottas finishing 0.3s in arrears.
Max Verstappen took third after spinning his Red Bull at the exit of the first corner – losing the rear as he swung past the apex, echoing the several spins he and teammate Alex Albon had in winter testing.
But he quickly got going again and used his softs to climb the order and end up 0.6s slower than Hamilton.
Sainz, Perez and Norris finished in positions four-six, with Albon and Ricciardo trailing them.
Kevin Magnussen took ninth for Haas, with Charles Leclerc rounding out the top 10 on the medium tyres, 1.1s slower than Hamilton in what was a low-key session for Ferrari.
Stroll finished 11th ahead of Vettel, with Esteban Ocon 13th for Renault but stepping out of his car early after it shed a piece of bargeboard bodywork as he ran down the main straight with 20 minutes to go, which required a brief virtual safety car to recover.
Several drivers – including Perez – had lock-ups at the tight up-hill right of Turn 3, but it was Turn 1 that appeared to be causing most problems, with Kimi Raikkonen (15th for Alfa Romeo) looking up and running deep there on two occasions.
Pierre Gasly (AlphaTauri) spun in front of George Russell at the final corner late on, which the Williams driver did well to avoid, and the pair finished P16 and P17.
Romain Grosjean brought up the rear of the field for Haas with just six laps on the board, as he missed most of the session after reporting a brake issue in the early stages, although he did appear for a final tour in the dying moments.