The Williams driver saved his best until the afternoon session where he posted a 1:23.261s effort on super-soft tyres.
Bottas' time proved to be 0.3s quicker the nearest rival Lewis Hamilton as Mercedes enjoyed another strong day in preparation for the Melbourne season opener.
The reigning world champion set his best time on soft compound tyres, while team-mate Nico Rosberg logged 91 laps in the afternoon as the Brackley team split its driving duties once again.
Renault enjoyed its strongest showing yet with Kevin Magnussen ending the day in third 0.6s shy of the pace.
Sebastian Vettel was fourth quickest as Ferrari racked up 151 laps on the medium tyres.
Despite a small suspension issue, McLaren showed encouraging signs with Jenson Button fifth fastest after 121 untroubled laps.
Red Bull focused its efforts on long stints which saw Daniel Ricciardo post the sixth fastest time ahead of Toro Rosso's Carlos Sainz and Force India's Sergio Perez.
Manor Racing's Pascal Wehrlein completed the top 10 ahead of Sauber's Marcus Ericsson, who caused the only red flag of the day when his new Sauber came to a halt on circuit.
Meanwhile, Haas F1's troubles continued with the American operation limited to just one lap after suffering a turbo issue.
Result: Formula 1 Pre-Season Test Day 2, Barcelona
|Red Bull/TAG Heuer