The pair made a perfect start to the two-part, combined qualifying session thanks to Talbot who topped the Am session.
There was an element of luck to it, though, with a timely red flag halting what would have been a better lap by Brad Schumacher (#74 MPC Audi).
Schumacher was coming around the last corner when the red flag was called due to teammate Yasser Shahin being stranded on the inside of that same corner.
The session was declared with Talbot ahead of Garth Walden (#45 RAM Motorsport Mercedes) and Schumacher.
The half-second gap between Talbot and Schumacher made the #65 hard to beat once the Pros jumped in for their session.
Effectively Kelvin van der Linde needed to find that half a second to topple Mostert, a job made even harder when there was another red flag with seven minutes to go when a Porsche Cup Car hit the wall on the way to Reid Park.
Once again the session was declared.
To that point van der Linde had only been able to made back two-tenths on Mostert, which sealed provisional pole for the #65 entry.
"We're not sure what the format is, it's been changing a fair bit," said Mostert.
"We're just happy. Liam did a fantastic job, gave me a couple tenths up my sleeve to make sure I got the car around. The balance of the car has been good. [Engineer] Adam [De Borre] has given us a good car. It's great."
The #74 MPC Audi ended up second ahead while Ricardo Feller was able to get the #777 MPC Audi from sixth based on Shahin's time to third.
The best non-Audi was the #75 SunEnergy Mercedes, driven by Jules Gounon in the Pro session, while the RAM Mercedes booked a spot in the heavily revised Shootout with the fifth best combined time.
Other cars to make it into the new-look Shootout were the #4 Grove Racing Porsche, the #55 Valmont Racing Mercedes, the #888 Triple Eight Mercedes, the #6 Wall Racing Lamborghini and the #9 MPC Audi.
Those 10 cars will take part in a two-part dash for pole later this afternoon, where cars 6-10 and 1-5 will each have 15 minutes to settle the first five rows of the grid.
The first of those sessions kicks off at 4:10pm local time.
Tune in to watch it live and free on Motorsport.tv (not available to viewers in Australia and New Zealand).
