Marc Marquez led a rain-soaked opening practice session for MotoGP's Japanese Grand Prix at Motegi, beating nearest rival Aleix Espargaro by almost nine tenths of a second.
In torrential conditions, Marquez was the rider to beat throughout Friday morning's 45-minute session, grabbing the top spot from title rival Maverick Vinales with a 1m58.303s around 15 minutes in.
The Repsol Honda rider proceeded to stretch his advantage at the head of the standings with a succession of hot laps, going 1.3s clear of the pack with a 1m57.194s and then opening the gap to almost two seconds with a 1m56.439s.
After a mid-session lull, Marquez's rivals started to close the gap, with Pramac Ducati rider Scott Redding surging to second with a time within two tenths of the Spaniard.
But after a fractional improvement to a 1m56.341s, Marquez ended the session with a best lap of 1m55.418s, putting him 0.875s up on Aprilia rider Espargaro, another late improver.
Redding held on to third, 1.099s off the pace, followed by the works Ducatis of Jorge Lorenzo and Andrea Dovizioso, who were split by 0.011s in fourth and fifth places.
Lorenzo's session came to a premature halt when he was collected at Turn 9 by Cal Crutchlow, who was seen remonstrating with the three-time champion in the gravel trap.
The LCR Honda rider was seventh-fastest, a place behind top Yamaha rider Johann Zarco in sixth, while Alex Rins - boosted by a new aerodynamic fairing on his Suzuki - Vinales and KTM's Bradley Smith completed the top 10.
Vinales' factory Yamaha teammate Valentino Rossi struggled to 19th place, 3.200s off the pace, while the second works Honda of Dani Pedrosa likewise endured a session to forget in 20th.
Tech 3 Yamaha rookie Kohta Nozane, deputising for an unwell Jonas Folger, held his own inside the top six in the early part of the session, but ended up dropping to 15th.
Fellow Japanese riders Katsuyuki Nakasuga (Yamaha) and Hiroshi Aoyama (standing in for Jack Miller at Marc VDS Honda) propped up the timesheets in 23rd and 24th places.
Tito Rabat (Marc VDS) and Andrea Iannone (Suzuki) both crashed during the session, while Danilo Petrucci suffered mechanical trouble with his Pramac Ducati early on but resumed on his second bike.