Wild won stage four, a twilight circuit race at Victoria Park, and that gave her the honours in a head-to-head duel this week with top Australian sprinter Chloe Hosking.
Wild (Cylance) also won the second stage on Sunday night, while Hosking rode superbly to win stage three.
Hosking (Ale Cipollini) was third on Tuesday behind compatriot Annette Edmondson (Wiggle High5).
But no-one was going to dethrone Spratt, the Orica-Scott captain.
“It’s a big sense of relief for me now and I am really, really happy to have won,” Spratt said. “The team were once again incredible today they had everything covered all race.
“They all said it was a harder race today than last year but I thought it was a lot easier, so it just shows how much work they did and I could just sit in and let them do everything for me again today.
“It was our goal to keep this jersey and we have done it, it really was a team effort so I am really happy we have also won the teams classification. I get to step up on the podium with the whole team and that is a really special moment for me.”
She won the opening stage and Orica-Scott then protected her overall lead for the rest of the tour.
Spratt was 22nd in Tuesday's bunch sprint and finished 25 seconds ahead of Dutch rider Janneke Ensing (Ale Cipollini) in the general classification, while Wild was third overall at 40 seconds.
It has been a flawless start to the year for Spratt, whose main aim is the Ardennes classics in the European spring.
She nearly lapped the field to win race two of the Bay Classic series and then finished second in a sprint finish with teammate Katrin Garfoot at the Australian championships road race.
At the end of this month, Spratt will defend her title at the Cadel Evans Great Ocean Rd race.