Both Bottas and the Scuderia’s Sebastian Vettel broke through the 1m 20s mark – faster than best lap ever posted during a Grand Prix weekend on the current layout of the circuit.
It was Bottas who emerged on top with a 1m 19.705s set on the ultrasoft tyre, a quarter of a second clear of Vettel, whose time came on the soft.
Their progress contrasted a disrupted day down at Williams, where 2017 rookie Lance Stroll – resuming following his costly day two error – suffered a spin in the morning and then hit the barriers at Turn 5 in the afternoon, bringing the team’s day to a premature close. The Canadian ended up ninth overall, 2.6s off Bottas’s pace.
Daniel Ricciardo’s afternoon was disrupted by exhaust issues, but he kept Red Bull on the heels of the frontrunners in third, just ahead of Renault duo Jolyon Palmer – whose morning stint included a spin into the gravel at Turn 3 – and Nico Hulkenberg, who took over for the afternoon and wound up three tenths off his new team mate.
Sauber’s Marcus Ericsson was sixth ahead of Lewis Hamilton – who assumed driving duties from Bottas in the afternoon – and Haas’s Romain Grosjean.
There was comfort for McLaren as Fernando Alonso racked up 72 laps, although the Spaniard could only manage 10th in the timesheets despite being the only driver other than Bottas to use the ultrasofts.
Toro Rosso’s Carlos Sainz and Daniil Kvyat sandwiched Force India’s reserve driver Alfonso Celis at the foot of the timesheets, with Sainz's day coming to an early conclusion due to drivetrain issues.
For a look back on the day’s events as they happened, click here.