The championship leader struggled for qualifying speed at Pukekohe just two weeks ago and admits that he has been battling to find a set-up direction for some time.
Winterbottom has been forced to close out the title without the help of team-mate Chaz Mostert, who had proved the pace-setter for much of the season before being injured in a crash at Bathurst.
Working with first-year race engineer Jason Gray, Winterbottom says a set-up change between sessions today provided encouraging results.
The apparent progress was made despite rain affecting the entire second session, leaving only a small window of slick tyre running.
“We've been chasing a direction on the car for a long time and that was the first real big progression forward that we've made,” said Winterbottom after topping practice.
“I'm pretty happy. Even though the day was mixed, to get a change in and actually have a good read, and the data looks good as well, it's nice.”
Winterbottom stressed that he has been working to set-up the car to his own driving style, which differs greatly from that of team-mate and Pukekohe race winner David Reynolds.
“It's clear that the cars are working because Scott (Pye) in New Zealand did a great job and so did Dave (Reynolds) and that's in the same car,” he said.
“It's hard to copy Dave because he's got quite a unique style, but Chaz, myself and Andre (Heimgartner) are normally pretty close.
“We've just been trying things. You don't want to go too far away from what you've got but today was nice.
“After the first session it was ok and the second, in areas I'd been chasing, it was actually really good.”
Bristling at suggestions that he has ‘tightened up' while trying to secure his first title, Winterbottom maintains that finding car speed is the only way to stay safe.
“If you have a quick car, qualify at the front and get a good start you're away from that pack,” he said, having been turned around while running mid-pack early in the Sunday race at Pukekohe.
“In New Zealand (in qualifying) I had a bit of a wobble in one corner and it lost me a tenth and a bit, which is about six spots. It puts you in the pack where you're vulnerable.
“If you're at the front you can control your own thing.
“(But) you can't just say ‘I'm going to do this', you've just got to see where you end up after quali.
“Back-to-back sessions means you could be at the front in one and at the back in the other if something goes wrong.
“Everyone just thinks you putt around (to bank points), but you're still trying to drive as good as you can to get up the front. You don't just slow down or anything.”
Winterbottom currently sits 239 points ahead of Reynolds and 240 clear of Craig Lowndes.