The Finn was just 0.050s faster than Lewis Hamilton, with a lap of 1m 09.848s compared to the Mercedes driver's 1m 09.898s.
Felipe Massa in the second Williams was just three thousandths of a second down the road in third, while Daniil Kvyat also got within 0.1s of Bottas as he jumped Toro Rosso into fourth place - much to team boss Franz Tost's delight - with a lap of 1m 09.927s.
That left an understeering Nico Rosberg, who believed his differential settings to be the cause of his handling problems, only fifth with 1m 09.999s.
Were Mercedes sandbagging, or has the nine-corner track really closed up the times? Qualifying will tell.
Fernando Alonso improved relative to FP2 to post 1m 10.054s for Ferrari, but dropped three places to sixth as he headed Daniel Ricciardo in the lead Red Bull on 1m 10.392s, Kevin Magnussen in the lone serviceable McLaren on 1m 10.449s, an understeering Kimi Raikkonen on 1m 10.488s in the other F14 T, Sebastian Vettel in the other Red Bull on 1m 10.562s, Nico Hulkenberg in the lead Force India on 1m 10.683s and Pastor Maldonado in the lead Lotus on 1m 10.776s.
The Venezuelan was still within one second of Bottas's benchmark.
Jean-Eric Vergne had a less satisfactory day than yesterday as a lap of 1m 11.043s left him 13th, ahead of Romain Grosjean in the second E22 on 1m 11.103s, Force India's Sergio Perez on 1m 11.235s, the tricky handling Saubers of Adrian Sutil and Esteban Gutierrez on 1m 11.294s and 1m 11.558s respectively, and Jules Bianchi's increasingly competitive Marussia on 1m 11.848s.
Kamui Kobayashi improved to 1m 12.320s for Caterham, ahead of team mate Marcus Ericsson on 1m 12.892s, with Max Chilton having problems en route to 1m 12.915s.
At the back Jenson Button only managed four laps and 1m 14.237s before losing engine braking and suffering a minor brake fire.
Once again there were a host of off-track moments, for Maldonado, Gutierrez, Raikkonen, Vergne, Perez, Ricciardo, Rosberg, Bianchi, Sutil, Magnussen and Alonso, while Kobayashi spun in the final moments while coming through Turn 9.
The biggest moment however befell Perez, when he ran wide and over the grass at the final turn and then got airborne over the bumps as he re-joined the track.