Testing began at 10am and concluded at 6pm, but a heavy rain storm soaked the track between 2-3pm.
After the rain a handful of riders - including Valentino Rossi, Dani Pedrosa and Andrea Dovizioso - chose to lap in the wet conditions.
Bright sunshine returned by 4pm, but the track still contained damp patches and most riders opted to remain in the pits and try again on day two.
All twelve manufacturer riders are present for the three-day test, plus the Forward Racing and BQR 'Claiming Rule Teams'.
Karel Abraham (Cardion AB) is struggling with a back injury sustained at the recent private Jerez test and missed day one.
The second Sepang test finishes on Thursday evening, after which only one more official test (at Jerez) will remain before the start of the racing season.
for pictures from the test.
1. Casey Stoner
AUS Repsol Honda 2m 1.761s
2. Dani Pedrosa
ESP Repsol Honda 2m 2.005s
3. Jorge Lorenzo
ESP Yamaha Factory Racing 2m 2.436s
4. Ben Spies
USA Yamaha Factory Racing 2m 2.819s
5. Alvaro Bautista
ESP San Carlo Honda Gresini 2m 2.959s
6. Nicky Hayden
USA Ducati Team 2m 3.132s
7. Cal Crutchlow
GBR Monster Yamaha Tech 3 2m 3.213s
8. Valentino Rossi
ITA Ducati Team 2m 3.245s
9. Hector Barbera
ESP Pramac Racing 2m 3.612s
10. Stefan Bradl
GER LCR Honda 2m 3.820s
11. Andrea Dovizioso
ITA Monster Yamaha Tech 3 2m 3.830s
12. Colin Edwards
USA Forward Racing (Suter-BMW CRT) 2m 5.510s
13. Franco Battaini
ITA Ducati Test Rider 2m 5.563s
14. Ivan Silva
ESP Avintia (FTR-Kawasaki CRT) 2m 8.479s
15. Yonny Hernández
COL Avintia (FTR-Kawasaki CRT) 2m 8.767s
Fastest Sepang I test times (Feb 2):
AUS Honda 1m 59.607s
ESP Yamaha 2m 0.198s
ITA Ducati 2m 0.824s
USA Suter 2m 4.722s
ESP FTR 2m 8.225s
Official Sepang MotoGP lap records:
ITA Yamaha 2m 0.518s
Fastest race lap:
AUS Ducati 2m 2.108s