The 30-year-old says this year's course is vastly different from the one she dominated in 2017 and admits the yellow jersey does bring added pressure.
"It's a very prestigious jersey to be wearing going into the race, but also it gives me a bit of confidence that I can stay with at least the best riders in Australia," Spratt said.
The 2018 tour has been upgraded to a UCI 2.1 event - just one level below the World Tour.
Among the start list will be 23-year-old Shannon Malseed, who upstaged some of domestic cycling's biggest names - including Spratt - to claim the national women's road title on Sunday.
Malseed, whose victory guaranteed her a spot in Australia's Commonwealth Games team, will ride for TIBCO-Silicon Valley Bank.
"Everything's a bit of a blur at the moment, meeting my new team and being on this massive high, so hopefully by tomorrow I've sort of settled down a bit," she said.
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Spratt said the breadth of Australian talent, and the possible threat to her title, extended far beyond Malseed.
"The Uni SA team here are a really strong line-up, they could be a national team in the world championships pretty much, so they're going to be really strong," she said.
"Being this time of the year, we're all in really great shape."
Lauren Kitchen, Grace Brown and Katrin Garfoot, who all finished in the top five at the road nationals, will also compete.
Stage one of the tour will start and finish in Gumeracha, about 37km from Adelaide, with a relatively gentle rolling course.
Race director Kimberley Conte said officials were prepared for the predicted high of 38C on Thursday.
A mobile command centre will be set up in Gumeracha and officials will liaise with emergency services throughout the day and the remainder of the event.