Needing to either finish better than eighth, or see his two nearest rivals fail to win the last race of the circuit, Museeuw can ill afford the dangers of a slippery road.
There is only an outside chance of rain at this stage in the course area, a hilly nature reserve about 100 kms north of Tokyo.
But at this time of the year in northern Japan the weather is unpredictable and squalls can sweep in quickly from the nearby coast.
The 179.5-km race, involving 12 circuits of 14.10 km and a final one of 10.30 km, is less testing than most of the 10 previous races in the 11-contest World Cup.
The greatest challenge -- and danger in wet weather -- is a an abrupt 200 metre high hill just one kilometre after the start of the circuit.
``That hill, particularly in wet weather, could throw even the most experienced cyclist,'' said a Japan Cup spokeswoman.
Museeuw, winner of the world road race title in Lugano, Switzerland, two weeks ago on his 31st birthday, has 162 World Cup points.
His Italian rivals for the title, Andrea Ferrigato on 126 points and Michele Bartoli on 124, need the 50 points from a first place finish to have any chance of beating Musseuw.
Even then, a high place finish by the Belgium would still deny them the title.
Museeuw has won only one World Cup race this year, the prestigious Paris-Roubaix in April, but with 65 race victories since turning professional in 1988, he has the experience to protect his lead.
It will be the first and last time a World Cup race will be held in Japan as the 11th race of the series, traditionally staged in Asia, will be scrapped from next year.
1. Mauro Gianetti (Switzerland) 4.31.01 2. Pascal Herve (France) 0.23 3. Andrea Peron (Italy) 0.24 4. Andrea Tafi (Italy) s.t. 5. Davide Rebellin (Italy) s.t. 6. Danielo Mardello (Italy) 0.32 7. Fabio Roscioli (Italy) 1.57 8. Viatcheslav Djavanian (Russia) 4.30 9. Michael Lafis s.t. 10. Bobby Jullich (U.S.) 4.42 11. Statano Faustini (Italy) 6.46 12. Daisuke Imanaka (Japan) 7.12 13. Stefano Zanini (Italy) 7.13 14. Fabian Jeker (Switzerland) 7.14 15. Valentinon Fois (Italy) 7.16 16. Stefano Cattai (Ita) + 7.17 17. Jurgen Werner (Ger) + 9.48 18. Peter Meinert (Den) + 9.49 19. Erik Breukink (Ned) + 9.50 20. Daniel Clavero (Spa) s.t. 21. Frigo (Ita) 22. Chiappucci (Ita) 23. Serrano (Spa) + 9.52 24. Santaromita (Ita) 25. Ferrigato (Ita) 26. Museeuw (Bel) + 9.53 27. Elli (Ita) + 9.57 28. Bugno. Outside time limit: Reiss (Usa). 133 starters, 28 finishers.
Museeuw's victory was automatically confirmed when his Italian rivals for the World Cup title, Andrea Ferrigato and Michele Bartoli, failed to win the last race of the 11-contest World Cup.
Musseuw, winner of the world road race title in Lugano, Switzerland, two weeks ago on his 31st birthday, finished 26th in the 179.5-km race. Ferriato finished 25th.
Before Sunday's race Musseuw had 162 World Cup points.
His Italian rivals Ferrigato on 126 points and Bartoli on 124 needed the 50 points from a first place finish to have any chance of beating Musseuw.
Museeuw has won only one World Cup race this year, the prestigious Paris-Roubaix in April, but he has 65 race victories since turning professional in 1988.
Mauro Gianetti of Switzerland won the Japan Cup after breaking away from the pack of six rival riders at the last eight km mark.
Pascal Herve of (France) finished second while Andrea Peron (Italy) captured the third place.
``I felt confident in winning the Japan Cup when I cleared the top of the hill in the last round,'' Gianetti said in reference to an abrupt 200 metre high hill just one kilometre after the start of the circuit.
Sunday's race involved 12 circuits of 14.10 km and a final one of 10.30 km that was considered less testing than most of the 10 previous races in the 11-contest World Cup.
It was the first and last time a World Cup race will be held in Japan as the 11th race of the series, traditionally staged in Asia, will be scrapped from next year.
Gianetti won the 179.5km (111.29 mile) race in 4hrs 31min 1sec. Pascal Herve of France was second, 23 seconds behind. Andrea Peron was third, 24 seconds behind the winn and just ahead of fellow-Italian Italians Andrea Tafi and Davide Rebellin.
"I studied the course and decided to make the break on the uphill climb on the final lap ... there was no point looking back," said Gianetti, for whom it was his third World Cup race win.
"It's very difficult to win a World Cup event and this is my last race with Team Polti," said the Swiss, winner of the Liege-Bastogne race in April, who will be joining a French team next season.
Seven riders were in contention when Gianetti Herve, Peron and Tafi made the first breakaway on the final lap of the 14.1km course before Gianetti made his last move.
Museeuw, who became world champion on his 31st birthday on October 13, finished 26th. He scored no points but already had the title secured for a second year running with his 162 points going into the race.
Italy's Andrea Ferrigato and Michele Bartoli could have beaten Museeuw if they had won the race. But Ferrigato was 25th while Bartoli did not come to Japan. Ferrigato finished with 126 points and was second overall. Bartoli was third on 124 points.
"I was concentrating on keeping my overall points lead to win the second World Cup title. That was my only target today," said Museeuw, who was among the frontrunners with Ferrigato early in the race.
"I'm still suffering from jetlag as I only arrived yesterday, but it's the same if I had come three days ago. I'm just tired after competing in so many races here, there and everywhere. It's a pity I see only hotels and courses," added the Belgian champion.
Claudio Chiappucci of Italy, three time Japan Cup winner from 1993 when it was not a World Cup event, finished 22nd in 4:40:51.
It was the first and the last time for Japan to host a World Cup race. The series will be reduced to 10 races next season.
1. Johan Museeuw (Bel) 162 pts 2. Andrea Ferrigato (Ita) 126 3. Michele Bartoli (Ita) 124 4. Andrea Tafi (Ita) 107 5. Stefano Zanini (Ita) 88 6. Mauro Gianetti(Sch) 87 7. Lance Armstrong (Usa) 81 8. Fabio Baldato (Ita) 77 9. Davide Rebellin (Ita) 68 10. Alexander Gontchenkov (Rus) 67 11. Gabriele Colombo (Ita) 58 12. Andrei Tchmil (Ukr) 56 13. Udo Bolts (Ger) 50 Pascal Richard (Sch) 50 Nicola Minali (Ita) 50 16. Glanluca Bortolami (Ita) 47 17. Richard Virenque (Fra) 46 18. Maximillan Sciandri (Gbr) 45 19. Vjatjeslav Ekimov (Rus) 44 Laurent Jalabert (Fra) 44
1. Mapei-GB (Ita) 101 pts 2. Motorola (USA) 61 3. MG-Technogym (Ita) 60 4. Festina-Watches (Fra) 54 5. Roslotto-ZG Mobili (Rus) 52 6. Team Polti (Ita) 43 7. Telekom (Ger) 40 8. T.V.M. (Ned) 23 9. Gewiss-Playbus (Ita) 22 10. Rabobank (Ned) 20.
1989 Sean Kelly (Irl) 1990 Gianni Bugno (Ita) 1991 Maurizio Fondriest (Ita) 1992 Olaf Ludwig (Ger) 1993 Maurizio Fondriest (Ita) 1994 Gianluca Bortolami (Ita) 1995 Johan Museeuw (Bel) 1996 Johan Museeuw (Bel)