The Movistar Yamaha rider topped the timesheets all day on the first day of the second batch of MotoGP testing at Sepang and afterwards said he was happy with the day's work.
Rossi was quoted by Motorsport.com: "The bike is a bit better in braking and corner entry and I think we need to work to understand the maximal potential, but the first test was good. I am happy to finish in the first position because I was in P1 from this morning, so it's a good first day.
Honda rider Dani Pedrosa was second fastest and he was keen to continue testing the setup on day two.
Pedrosa said: "Today we focused on testing different setups for the bike and I think it went well. We have not tried any new parts, instead confirming our findings with what we had at the last test, even though the track was not perfect.
"It rained at the end, so we could also ride a little in those conditions. Tomorrow we will continue testing some changes to the setup, to see if we can come up with some improvements that allow us to ride more comfortably."
Times (Day 1, test 2):
1. Valentino Rossi (Yamaha) 2m00.414s
2. Dani Pedrosa (Honda) 0.129s
3. Pol Espargaro (Yamaha) 0.462s
4. Aleix Espargaro (Suzuki) 0.641s
5. Jorge Lorenzo (Yamaha) 0.748s
6. Marc Marquez (Honda) 0.776s
7. Cal Crutchlow (Honda) 0.808s
8. Bradley Smith (Yamaha) 0.827s
9. Maverick Vinales (Suzuki) 0.903s
10. Andrea Dovizioso (Ducati) 0.941s
11. Scott Redding (Honda) 1.178s
12. Alvaro Bautista (Aprilia) 1.326s
13. Hector Barbera (Ducati) 1.512s
14. Nicky Hayden (Honda) 1.648s
15. Andrea Iannone (Ducati) 1.728s
16. Danilo Petrucci (Ducati) 1.811s
17. Karel Abraham (Honda) 1.980s
18. Stefan Bradl (Forward Yamaha) 1.996s
19. Yonny Hernandez (Ducati) 2.192s
20. Eugene Laverty (Honda) 2.316s
21. Mike di Meglio (Ducati) 2.527s
22. Jack Miller (Honda) 2.592s
23. Michele Pirro (Ducati) 2.691s
24. Loriz Baz (Forward Yamaha) 2.902s
25. Katsuyuki Nakasuga (Yamaha) 2.923s
26. Alex de Angelis (Aprilia ART) 3.552s
27. Marco Melandri (Aprilia) 3.586s