Mostert tops opening day in Sydney
Mostert has been a constant threat to Winterbottom with his unrivalled qualifying speed but has been unable to convert a fast Ford into strong starts and consistent race results.
The 23-year-old has more podiums than anyone this year but sits 292 points behind his team-mate with Red Bull Racing's Craig Lowndes wedged between them. A third FG-X Falcon of David Reynolds is 32 points further adrift.
As he has done consistently this year Mostert was at the top of the time sheets in practice at the Sydney Motorsport SuperSprint today, ahead of Supercheap Auto Racing's Tim Slade and Kiwi Shane van Gisbergen.
Mostert had denied the Prodrive Racing outfit will enforce team orders favoring Winterbottom in order to claim their, and his, maiden Championship.
"As far as I know we're all pushing for the Championship, we've all got our own races to run," Mostert said.
"Prodrive has always left that open; even last year when Frosty was leading the championship. It's a different situation this year though as we've got a better package going into the enduros.
"I haven't been told any team orders unless you have. For me I'm just going out there trying to win as many races as I can and trying to get as many Championship points as I can."
Even with his strong practice session Mostert felt his car could be improved markedly ahead of tomorrow's two sprint races and Sunday's longer fixture.
"We're pretty unhappy with the car to be honest," he said. "It's pretty wild out there I don't know if it's the track or the car but a bit of work to do tonight but I'm still happy to be up the pointy end of the timesheets.
"It's strange normally our hard car feels better than our soft car but today our soft car feels better so hopefully there's some positive stuff going into the weekend.
"We've got one more practice tomorrow which we can try to do some last set up changes and make it better – it's good to finish off today at the top but we've got a little bit of work to do."
Van Gisbergen, second in last year's Championship, hopes for a better outcome than what has been an enormously frustrating year for the young Kiwi.
"Our car has been a bit of a battle the last few rounds so trying a whole lot of things and a different direction to make it work so it's a bit of a struggle to be honest," he said.
"It has been a bit frustrating but we're working hard trying so many different things and backing our own directional set up. I'm not completely happy but it is better."
Winterbottom finished the session fifth, behind Nick Percat, who earned his first solo podium at the circuit last year.
The Red Bulls were back in the pack, Jamie Whincup 13th and Lowndes 19th – technical director Ludo Lacroix said they were searching for grip and assessing "new bits and pieces".
Holden Racing Team co-driver Jack Perkins took part in the session in the #22 Commodore, with James Courtney out of the car for medical reasons.
Courtney was hit by a piece of debris that loosened by a Navy helicopter conducting a display at the event. He was subsequently transported to Westmead Hospital for further assessment.
The Royal Australian Navy and V8 Supercars have commenced investigations into the incident.
Results
| Pos | Driver | Team | Fastest | Gap | Lap | Of |
| 1 | 6 Chaz Mostert | Pepsi Max Crew | 1:29.9026 | 0.0000s | 12 | 22 |
| 2 | 47 Tim Slade | Supercheap Auto Racing | 1:30.0291 | 0.1265 | 21 | 22 |
| 3 | 97 Shane van Gisbergen | Team Darrell Lea STIX | 1:30.0915 | 0.1889 | 16 | 16 |
| 4 | 222 Nick Percat | Repair Management Aust Racing | 1:30.3143 | 0.4117 | 16 | 16 |
| 5 | 5 Mark Winterbottom | Pepsi Max Crew | 1:30.3681 | 0.4655 | 16 | 19 |
| 6 | 33 Scott McLaughlin | Wilson Security Racing GRM | 1:30.4286 | 0.5260 | 10 | 22 |
| 7 | 111 Andre Heimgartner | Super Black Racing | 1:30.4586 | 0.5560 | 17 | 23 |
| 8 | 23 Michael Caruso | Nissan Motorsport | 1:30.4894 | 0.5868 | 17 | 18 |
| 9 | 18 Lee Holdsworth | Walkinshaw Performance | 1:30.5614 | 0.6588 | 15 | 25 |
| 10 | 55 David Reynolds | The Bottle-O Racing Team | 1:30.6609 | 0.7583 | 13 | 18 |
| 11 | 2 Garth Tander | Holden Racing Team | 1:30.7549 | 0.8523 | 18 | 19 |
| 12 | 9 Will Davison | Erebus Motorsport V8 | 1:30.7807 | 0.8781 | 23 | 23 |
| 13 | 1 Jamie Whincup | Red Bull Racing Australia | 1:30.8443 | 0.9417 | 22 | 23 |
| 14 | 34 David Wall | Wilson Security Racing GRM | 1:30.9237 | 1.0211 | 17 | 22 |
| 15 | 8 Jason Bright | Team BOC | 1:30.9311 | 1.0285 | 11 | 21 |
| 16 | 15 Rick Kelly | Nissan Motorsport | 1:30.9369 | 1.0343 | 19 | 20 |
| 17 | 7 Todd Kelly | Nissan Motorsport | 1:30.9502 | 1.0476 | 18 | 19 |
| 18 | 17 Scott Pye | DJR Team Penske | 1:30.9566 | 1.0540 | 18 | 19 |
| 19 | 888 Craig Lowndes | Red Bull Racing Australia | 1:30.9878 | 1.0852 | 22 | 23 |
| 20 | 22 Jack Perkins | Holden Racing Team | 1:31.0918 | 1.1892 | 18 | 20 |
| 21 | 14 Fabian Coulthard | Freightliner Racing | 1:31.2937 | 1.3911 | 14 | 23 |
| 22 | 21 Dale Wood | GB Galvanizing Racing | 1:31.3526 | 1.4500 | 13 | 24 |
| 23 | 99 James Moffat | Nissan Motorsport | 1:31.7131 | 1.8105 | 15 | 18 |
| 24 | 4 Ash Walsh | Erebus Motorsport V8 | 1:31.8255 | 1.9229 | 15 | 17 |
| 25 | 3 Tim Blanchard | Team Cooldrive | 1:32.3520 | 2.4494 | 21 | 21 |