Carlos Sainz set the fastest time in a wet first practice session at the Japanese Grand Prix, making the most of a brief respite in the conditions to go fastest on the intermediate tyres.
The first few drivers to venture out on track were greeted by rivers flowing across some of the corners, but conditions gradually improved as more and more cars went out on full wet tyres. Roughly an hour into the session the rain eased up and a number of drivers managed a lap on the intermediate tyres, including Sainz in the Toro Rosso who went 0.504s quicker than his nearest rival Daniil Kvayt. The rain increased in intensity in the final 15 minutes, forcing most drivers to return to the safety of the full wet tyres, resulting in slower lap times.
Nico Rosberg was the fastest driver on the full wet tyres with a time 0.643s off Sainz, but a good lap was as much about timing a run in the conditions as it was about the car underneath the driver. Sebastian Vettel set his fastest time on intermediates and was third fastest ahead of Lewis Hamilton, who only ventured out for a timed lap in the final 15 minutes on full wet tyres.
Several cars went off track during the 90 minute session, but none found the barriers. Valtteri Bottas went wide at 130R, the two Saubers ran off the track at Spoon and Felipe Massa took a trip through the gravel at the second Degner. The Williams pair appeared to be working on their car's wet set-up, which has been a weakness this year, but complaints from both drivers and times over two seconds off the pace suggest little in the way of progress was made.
Jenson Button was the slowest of the drivers to set a time, 6.244s off pace after six laps on the full wet tyres. Several drivers opted to set just one installation lap, including the two Lotus drivers Pastor Maldonado and Jolyon Palmer as the team opted not to risk an accident and an expensive repair bill.