The Yamaha Factory Racing entry that includes MotoGP team-mates Bradley Smith and Pol Espargaro set the pace during Thursday practice for the Suzuka 8 Hours.
The Tech 3 riders have been called up to join Japanese champion and MotoGP podium finisher Katsuyuki Nakasuga for Yamaha's first factory Suzuka assault since 2002.
The trio, racing with the #21, got off to an excellent start by topping the Group A practice sessions and setting the best overall time of the day with a 2m 7.282s.
That kept them a massive 0.972s clear of nearest Group A rivals #104 Toho Racing with Moriwaki, which includes former Moto2 champion Toni Elias and present Moto2 racer Ratthapark Wilairot
Third quickest in Group A was the #634 machine of reigning champions Musashi RT Harc-Pro - Honda's factory entry, which this year features retired double MotoGP champion Casey Stoner.
The Australian is making his motorcycle racing return alongside WSBK star Michael van der Mark and Honda test rider Takumi Takahashi, who have won the last two Suzuka races with Leon Haslam.
The #634 made a late climb up the timesheets to finish the second session 1.180s behind the pace-setting R1 with a time of 2m 8.462s. The #21 and #634 bikes had been fifth and sixth respectively in the opening Group A session, held on a damp track.
According to Borja Gonzalez
, all three of the #21 Yamaha riders lapped in the 2m 7s, with Espargaro the fastest, while Stoner clocked the quickest time for the #634 Honda team.
Thursday's Group B practice sessions were both led by the #12 Yoshimura Suzuki entry of WSBK's Alex Lowes, BSB's Josh Waters and home rider Takuya Tsuda - a best lap of 2m 8.403s putting them third on combined times.
The #778 FCC TSR Honda of Moto2's Dominique Aegerter, WSS rider Kyle Smith and Australian Josh Hook was just 0.035s slower than the Yoshimura bike for second in Group B and fourth overall, a fraction in front of the #634 Honda.
The Team Kagayama (Suzuki) bike of Japanese stars Yukio Kagayama, Noriyuki Haga and Ryuichi Kiyonari was fifth fastest in Group A with a 2m 8.660s. The Monster Energy Yamaha-YART line-up of Broc Parkes, Ivan Silva and Sheridan Morais took tenth.
Honda has won the Suzuka 8 Hours for the last five years in a row, and been beaten just twice in the last 18 years. By contrast, Yamaha's most recent Suzuka win was with Colin Edwards and Noriyuki Haga in 1996. Suzuki last won in 2009, with Kawasaki winless since 1993.
The Suzuka circuit was dropped from the MotoGP calendar after 2003, meaning Smith and Espargaro will be making their race debuts this weekend. Stoner made two Suzuka starts as a 125GP rider.
Further practice and qualifying takes place on Friday and Saturday, with the race on Sunday.
Suzuka 8 Hours: Top 5 combined Thursday practice times:
1. Yamaha Factory Racing Team Pol Espargaro, Bradley Smith, Katsuyuki Nakasuga
(#21) 2m 7.282s
2. Toho Racing with Moiwaki Toni Elias, Ratthapark Wilairot, Tatsuya Yamaguchi
(#104) 2m 8.254s
3. Yoshimura Suzuki Shell Advance Alex Lowes, Josh Waters, Takuya Tsuda
(#12) 2m 8.403s
4. FCC TSR Honda Dominique Aegerter, Kyle Smith, Josh Hook
(#778) 2m 8.438s
5. Musashi RT Harc-Pro Casey Stoner, Michael van der Mark, Takumi Takahashi
(#634) 2m 8.462s