Maverick Vinales briefly knocks Jorge Martin from the top, but the #89 strikes straight back with a 1m 29.266s on a soft rear tyre, putting him half a second clear of the field.
Bagnaia again makes a mistake under braking into Miller corner (Turn 4) and takes the long lap penalty loop. He's now looking at his right hand, perhaps some sort of glove issue?
Currently at the bottom of the timesheets are Fabio Quartararo, Franco Morbidelli, Miguel Oliveira, Luca Marini and Joan Mir.
Rookie Augusto Fernandez pops up to third, an impressive lap by the GASGAS Tech3 rider that puts him between Vinales and Binder.
Last year's winner Alex Rins has fallen at Siberia (Turn 6), after losing the front of his LCR Honda. Fortunately, Rins, who completed his first races since May's leg fractures in Indonesia last weekend, walks away unharmed.
Aprilia's Maverick Vinales is closing on Martin at the top, but keeps losing out in the final sector. Now +0.211s from the Pramac Ducati.
Halfway through opening practice and it's title contender Jorge Martin as the only rider in the 1m 29s, currently 0.4s clear of Brad Binder.
Title leader Francesco Bagnaia is eighth (+0.720s) and home hero Jack Miller 11th (+0.850s).
Marc Marquez is back in the pits.
15mins gone, top 12: Martin, Binder, Zarco, A.Marquez, Bezzecchi, Vinales, Bastianini, Bagnaia, M.Marquez, P.Espargaro, A.Espargaro, A.Fernandez
That's Marquez's 24th fall of the season and comes after two DNFs in Mandalika. The Repsol Honda rider had been hoping to rebuild confidence at Phillip Island...
Marc Marquez is down! The 2022 runner-up is the first faller of the weekend, losing the front under braking at Turn 10, the MG Hairpin, after Lukey Heights.
Big slide for Luca Marini out of the fast final corner. Marini saves the near highside when the tyre grips, and is narrowly missed by the following Bagnaia. Marini is already riding with a recently fractured collarbone.
Pramac Ducati riders Jorge Martin and Johann Zarco bring the lap times down to the low 1m 30s, while Francesco Bagnaia goes wide under braking for turn 4, shaking his wrist as he takes to the long lap penalty loop.
The Aprilia RS-GP has often gone well at the fast and flowing Phillip Island... it's Maverick Vinales leading Aleix Espargaro after the opening laps.
The green flags are waved and FP1 begins.
Meanwhile, Marc's younger brother Alex is back on his Gresini Ducati to again try and return from broken ribs having been forced to abandon a return, due to the pain, last weekend in Indonesia.
Marquez's 2013 race lap record is from the 'pit stop' race in his rookie season, where all riders were forced to change (Bridgestone) tyres during the race due to wear problems on the new asphalt. Marquez actually came in too late and was black-flagged, but still went on to win the title.
Here are the official Phillip Island lap records although, as a reminder, FP1 is a free practice and only this afternoon's second session will decide the top ten riders with direct Qualifying 2 access:
Official Phillip Island MotoGP records
Best lap: Jorge Martin 1m 27.767s (2022)
Fastest race lap: Marc Marquez 1m 28.108s (2013)
Extreme weather might be forecast for Sunday, but bright and sunny conditions greets the start of the Australian MotoGP weekend. Opening MotoGP practice starts in 5mins.