The lead Ferrari of Sebastian Vettel and the other Silver Arrow of Lewis Hamilton completed the top five.
As expected, early rain made for treacherous conditions. All the drivers ventured out for assessment laps, but it took almost an hour before Max Verstappen became the first driver to get a timed lap on the board for Toro Rosso. The Dutchman's team mate Carlos Sainz headed out too and managed 1m 53.741s, exactly 2s down on Verstappen's benchmark.
Felipe Massa (BRA) Williams FW37 at Formula One World Championship, Rd14, Japanese Grand Prix, Practice, Suzuka, Japan, Friday 25 September 2015. © Sutton Motorsport Images
Suddenly the track became busy, and as conditions gradually eased, times began to fall. Williams were the first team to try the green-marked intermediate tyre, and Felipe Massa immediately went fastest in the first sector - but a major moment for Valtteri Bottas showed that other parts of the track were still incredibly wet. Bottas later went off at 130R and Massa slipped off into the gravel at Turn 9 - he was able to rejoin - to highlight just how tricky conditions were.
Mercedes' Nico Rosberg then hit the front, before improving his own benchmark to work down to a 1m 50.077s on the wet tyre. That wouldn't stand for long however: five minutes later Verstappen went out on intermediates, immediately set the fastest time in sector one, and eventually slotted into second on 1m 50.940s. Intermediates were suddenly the tyre of choice, and both Red Bull's Daniil Kvyat and Sainz were out on the green-marked tyre.
The duo capitalised: Kvyat went quickest, only to be demoted by Sainz moments later. Their window was fleeting, with Sainz reporting more aquaplaning shortly after as the rain worsened once more, ensuring the Spaniard topped an F1 session for the first time in his short career.
Rosberg's time therefore stood up for third, ahead of Vettel and Hamilton, who set his fastest time on the wet tyre in the final 15 minutes. Verstappen's time left him sixth, fractionally ahead of Kimi Raikkonen in the second Ferrari. Massa and Bottas were eighth and 10th respectively, split by Sauber's Marcus Ericsson.
Like Ericsson, Felipe Nasr in the second Sauber also set his fastest time on inters, and wound up 11th ahead of McLaren's Jenson Button, who was 6s off the pace after one early flying lap early on the wets.
Red Bull's Daniel Ricciardo and McLaren's Fernando Alonso were among the 10 drivers who opted not to set a time. The same was true of Force India's Sergio Perez and Nico Hulkenberg, Marussia's Alexander Rossi and Will Stevens, and Lotus's Pastor Maldonado and Jolyon Palmer - the latter pair managing just one exploratory lap each in a very cautious start to the weekend.
There were several off-track incidents, most notably at Spoon Curve where numerous drivers ran wide. However, Massa was the only driver to trip through the gravel after a small moment at Turn 9.
