Supercheap Auto Racing has endured a tough start to the Sydney 500, finishing 17th in race 28.
A hard-hitting opening lap saw Chaz drop to ninth place from his eighth place starting position on the streets of Sydney.
Mostert was among the group of cars to pit early, while looking for a late-race advantage.
Tyre life and driver error hampered performance, with incidents both early and late in the race pushing Mostert down the field.
Despite running 13th in the final quarter, further problems saw Chaz falls to 17th on the final lap.
Chaz Mostert - #55 Supercheap Auto PRA Ford:
Race 28: 17th
“I didn’t have a very good day today. I drove like a bit of a rookie and just made too many errors. It was a pretty feisty race from the start and had plenty of battles throughout. I locked up a couple of times and ended down the escape road which cost me a few places each time and then at the end I was battling a guy with better tyres and came off second best. All of that aside we learnt a lot today so I plan to come out and have a big crack tomorrow.”
Rod Nash – Team Owner:
"It was disappointing to finish the day the way we did. Chaz was in a reasonable position in the last quarter of the race but tyre life hasn't been our strong point all season so we'll go back to the drawing board and see if we can pull something out of a hat for tomorrow. It's going to be another hot one and at this track anything can happen so we'll keep our fingers crossed for one last podium."
1) Jamie Whincup – Triple Eight
2) Garth Tander - HRT
3) Shane van Gisbergen – Triple Eight
4) Scott McLaughlin – Garry Rogers Motorsport
5) James Courtney - HRT
17) Chaz Mostert – Prodrive Racing
DRIVER CHAMPIONSHIP POINTS
1) Shane van Gisbergen – Triple Eight: 3218
2) Jamie Whincup – Triple Eight: 3048
3) Scott McLaughlin – Garry Rogers Motorsport: 2695
4) Craig Lowndes – Triple Eight: 2686
5) Will Davison – Tekno: 2499
7) Chaz Mostert – Prodrive Racing: 2289
1) Triple Eight: 6276
2) HRT: 4194
3) GRM: 4061
4) Prodrive Racing Australia: 3893