The German-Australian squad ran a slightly longer first stint to pinch track position as their key rivals fought on the road, with Ayhancan Guven behind the wheel in top spot just after the first Safety Car period of the day at Mount Panorama.
The #130 GruppeM Racing Mercedes-AMG sits second in the hands of Felipe Fraga, but has just been hit with a drive-through penalty for a rear wing adjustment while being refuelled.
Third is the #46 Team WRT BMW with Raffaele Marciello behind the wheel, then Dries Vanthoor in the sister #32 BMW and the #888 Triple Eight Race Engineering Mercedes-AMG of Broc Feeney – all three with a strategic advantage due to a stop under the recent yellow.
The #13 Phantom Global Racing Porsche has risen to sixth, from the #75 SunEnergy1 Mercedes-AMG, the #2 Melbourne Performance Centre Audi, the #22 MPC Audi, and the #77 Craft-Bamboo Racing Mercedes-AMG which is last of those on the lead lap in 10th position.
He headed Mikael Grenier in the #888 Triple Eight Mercedes-AMG by about 1.5s in the opening racing laps, with Maro Engel (#130 GruppeM Mercedes-AMG) third from Laurens Vanthoor (#912 Manthey EMA Porsche), Luca Stolz (#75 SunEnergy1 Mercedes-AMG), and Ricardo Feller (#2 MPC Audi).
Maxime Martin (#46 WRT BMW) outbraked Kelvin van der Linde (#22 MPC Audi) for seventh on the outside line to Griffins Bend on Lap 5, while Pro-Am pole-sitter Harry King (#911 Manthey EMA Porsche) continued to run ninth and #88 Jamie Whincup (Triple Eight JMR Mercedes-AMG) in 10th.
The race-leading #32 BMW caught traffic on just Lap 6 while Triple Eight’s Grenier had cut van der Linde’s margin to 0.65s on Lap 10.
Both had gapped the #130 GruppeM Mercedes-AMG by three seconds at one point, before the top 10 compressed again towards the end of the first hour.
Maximilian Goetz was running just behind in 11th in the #77 Craft-Bamboo Mercedes-AMG while, 15 seconds further back, Jaxon Evans had dragged the #13 Phantom Global Porsche from 18th to 12th.
The sun was out when the first hour elapsed during Lap 27, at which point the #32 BMW led by 1.02s over the #888 Mercedes-AMG, with the #130 Mercedes-AMG and the #912 Porsche another second behind.
The scheduled pit stops started on Lap 30, with Sheldon van der Linde and Grenier were among those to come in on Lap 31.
The #32 WRT BMW was dispatched on new, cold tyres and Charles Weerts had to withstand pressure from Will Brown on used, warm tyres in the #888 Triple Eight Mercedes-AMG.
The #46 BMW jumped them when Martin handed over to Valentino Rossi on Lap 32, with the MotoGP champion then coming under huge pressure from WRT team-mate Weerts as he waited for his rubber to come up to temperature.
With Manthey EMA keeping its Porsches out for a lap longer, the squabble cost WRT BMW the lead, with Guven emerging the new front-runner in the #912 911 GT3 R.
Once the order settled again, it was Guven from David Reynolds in the #130 GruppeM Mercedes-AMG, Jules Gounon in the #75 SunEnergy1 Mercedes-AMG, Rossi, Weerts, Brown, Markus Winkelhock in the #2 MPC Audi, Liam Talbot in the #22 MPC Audi, and Jayden Ojeda in the #77 Craft-Bamboo Mercedes-AMG.
Yasser Shahin dropped from second to 10th on his stone cold tyres in the #911 Porsche, but was still leading the Pro-Ams, with Prince Jefri Ibrahim 11th in the #88 Triple Eight JMR Mercedes-AMG.
Jessie Bryan led in GT4 in 24th outright in the #25 Method Motorsport McLaren which was started by Chaz Mostert.
By the time the second hour had ticked into the third, Guven in the #912 Porsche led on Lap 55 by 4.67s from Reynolds in the #130 Mercedes-AMG, then the #75 Mercedes-AMG, the #46 BMW, the #32 BMW, the #888 Mercedes-AMG, and the #2 Audi in seventh.
Ojeda was almost 22 seconds further back in eighth in the #77 Mercedes-AMG, from Joel Eriksson in the #13 Porsche, Talbot in the #22 Audi, Luke Youlden in the #44 Valmont Racing/Tigani Motorsport Audi which was leading the Silver class, and Craig Lowndes in 12th in the #222 Mercedes-AMG, while Ibrahim had just dropped off the lead lap in 15th in the #88 Mercedes-AMG.
Weerts was able to grab fourth from WRT BMW team-mate Rossi when the latter ran wide at Murray’s Corner on Lap 57.
Youlden kicked off the second pit stop cycle on Lap 60, with Weerts in from fourth and Brown from sixth in on Lap 63.
Gounon, who had been stalking Reynolds for some time, pitted from third on Lap 64 and was followed in by Rossi.
The top two of Guven and Reynolds, by then almost 10 seconds apart, largely completed the cycle on Lap 65.
Guven was still the leader when he rejoined in the #912 Manthey EMA Porsche, by a dozen seconds and growing, from Fraga in the #130 GruppeM Mercedes-AMG, Marciello in the #46 WRT BMW, Dries Vanthoor in the #32 WRT BMW, Brown in the #888 Triple Eight Mercedes-AMG, Kenny Habul in the #75 SunEnergy1 Mercedes-AMG after a long pit stop, Ojeda in the #77 Craft-Bamboo Mercedes-AMG, Bastian Buus in the #13 Phantom Global Porsche, Christopher Haase in the #22 MPC Audi, and Brad Schumacher in the #2 MPC Audi, which was last on the lead lap in 10th.
Lowndes ran 11th in the #222 STM Mercedes-AMG, from Marcel Zalloua in the #44 Valmont/Tigani Audi leading the Silver class, and Garth Walden in the #48 M-Motorsport Mercedes-AMG leading the Pro-Am class in 13th outright, with Jordan Love 15th in the #88 Mercedes-AMG.
Guven bolted to a 20-second lead early into his second straight stint and was still 15 seconds to the good when the first Safety Car period of the day came on Lap 74, due to the Invitational class Vortex spinning into the McPhillamy Park gravel trap in the hands of Julien Boillot.
MPC pitted Haase for an almost free stop, before WRT called both Marciello and Dries Vanthoor in, as did Triple Eight to swap Brown for Feeney, with those three cars maintaining third through fifth respectively.
The order was thus the #912 Porsche, the #130 Mercedes-AMG, the #46 BMW, the #32 BMW, the #888 Mercedes-AMG, the #13 Porsche, the #75 SunEnergy1 Mercedes-AMG, the #2 Audi, the #22 Audi, and the #77 Mercedes-AMG in 10th after Ojeda also stopped under yellow.
The restart came on Lap 78, with 177 minutes elapsed, as Guven took a 1.58-second lead across the stripe thanks to traffic behind him.
The #25 Method McLaren still led in GT4, with Marcos Flack in the seat.