Danilo Petrucci opened the Phillip Island test quickest for his Pramac Duacti team on Wednesday morning, though wet weather persisted throughout the day, limiting on-track time.
The opening hour saw no action at all as everyone decided it was best to remain dry in the garage and wait for the rain to clear. However as it became apparent the rain was going to remain for some time, a few riders ventured out.
Honda's Cal Crutchlow was first out, posting a 1m39.168s before much of the field joined him on-track during a brief break in the rain.
That break allowed Marc Marquez to go top with a time four-seconds quicker than Crutchlow using the new Michelin intermediate tyre.
Improvements looked unlikely as the rain returned once again, but some minor respite allowed Petrucci to fly, posting a 1m32.769s to go top before improving by over a second to end the day quickest.
Suzuku's Maverick Vinales also used the drier conditions at the end to jump up the order, finishing second quickest ahead of Yamaha's Bradley Smith and the second Pramac of Scott Redding.
Jack Miller, back from an injury, was ninth-quickest despite missing the opening Sepang test a fortnight ago. His Marc VDS team-mate Tito Rabat was 11th.
MotoGP Phillip Island Test Times – Day One:
| Pos | Rider | Team | Laptime | Gap | Laps |
| 1 | Danilo Petrucci | Octo Pramac Yakhnich | 1:31.764 | 12 | |
| 2 | Maverick Vinales | Team Suzuki Ecstar | 1:32.483 | 0.719 | 20 |
| 3 | Bradley Smith | Monster Yamaha Tech 3 | 1:32.590 | 0.826 | 27 |
| 4 | Scott Redding | Octo Pramac Yakhnich | 1:32.864 | 1.100 | 41 |
| 5 | Cal Crutchlow | LCR Honda | 1:32.948 | 1.184 | 21 |
| 6 | Valentino Rossi | Movistar Yamaha MotoGP | 1:33.088 | 1.324 | 27 |
| 7 | Pol Espargaro | Monster Yamaha Tech 3 | 1:33.126 | 1.362 | 20 |
| 8 | Yonny Hernandez | Aspar MotoGP Team | 1:33.841 | 2.077 | 6 |
| 9 | Jack Miller | Marc VDS Racing Team | 1:33.992 | 2.228 | 6 |
| 10 | Andrea Iannone | Ducati Team | 1:34.049 | 2.285 | 9 |
| 11 | Tito Rabat | EG 0.0 Marc VDS | 1:35.273 | 3.509 | 29 |
| 12 | Marc Marquez | Repsol Honda Team | 1:35.354 | 3.590 | 20 |
| 13 | Aleix Espargaro | Team Suzuki Ecstar | 1:35.584 | 3.915 | 2 |
| 14 | Eugene Laverty | Aspar MotoGP Team | 1:35.679 | 4.402 | 10 |
| 15 | Takuya Tsuda | Suzuki Test Team | 1:36.166 | 4.402 | 6 |
| 16 | Jorge Lorenzo | Movistar Yamaha MotoGP | 1:39.825 | 8.061 | 24 |
| 17 | Dani Pedrosa | Repsol Honda | 1:40.138 | 8.374 | 15 |
| 18 | Andrea Dovizioso | Ducati Team |
