Alonso fastest in wet Japanese first practice with Verstappen sixth
Two-time world champion Alonso braved steady rain at the Suzuka circuit to streak round in 1min 42.248sec for Alpine - 0.315sec quicker than second-placed Carlos Sainz of Ferrari.
Verstappen can claim the title on Sunday if he wins the race with the fastest lap, no matter what his rivals do, but he put in only a short stint in first practice.
The Red Bull runaway leader did not enter the fray until halfway through and clocked a best time of 1min 43.362sec.
Ferrari's Charles Leclerc, Verstappen's nearest rival in the championship standings, had the third-fastest time in 1min 42.634sec.
Alonso's Alpine teammate Esteban Ocon was fourth, Kevin Magnussen was fifth with Haas, and Mick Schumacher was seventh behind Verstappen.
Schumacher had the biggest moment of the session when he spun into the barriers and onto the grass after the chequered flag, destroying his front wing.
The wet conditions sent huge sprays off the back of each car and Japanese driver Yuki Tsunoda reported "a couple of rivers" on one section on an early lap.
Seven-time world champion Lewis Hamilton was 2.31sec behind Alonso in 13th place, while Mercedes teammate George Russell was 18th after an oil leak.
Top-10 times from first practice session at the Japanese Grand Prix on Friday:
1. Fernando Alonso (ESP/Alpine) 1:42.248, 2. Carlos Sainz (ESP/Ferrari) 1:42.563, 3. Charles Leclerc (MON/Ferrari) 1:42.634, 4. Esteban Ocon (FRA/Alpine), 5. Kevin Magnussen (DEN/Haas) 1:43.258, 6. Max Verstappen (NED/Red Bull) 1:43.362, 7. Mick Schumacher (GER/Haas) 1:43.761, 8. Lando Norris (GBR/McLaren) 1:43.889, 9. Valtteri Bottas (FIN/Alfa Romeo) 1:43.969, 10. Sergio Perez (MEX/Red Bull) 1:44.234
