The defending champion had banked on his trademark attack to secure overall victory but didn’t bet on dark horse Daryl Impey (Mitchelton-Scott), who finished second to tie with Porte on overall time and now leads the race on countback.
Porte was gracious in victory and defeat behind the podium where he spoke with press, looking much further afield than the final podium of the WorldTour opener.
“I had a tough end of last year so to be up here and win Willunga for a fifth time in a row, I have to say I’m happy but of course I would have loved to win the overall,” Porte said.
The 32-year-old was billed as Froome’s greatest challenger at the Tour de France last year, but crashed out of stage nine with a broken collarbone and pelvis.
Watch: Tour Down Under stage five highlights
The Tour Down Under has doubled as the Australian’s return to stage racing following the high-speed collision and tedious recovery.
“I have a fantastic bunch of people around me, from my team to wife and family,” he said.
“It has been a tough time, it was a nasty crash, it knocked me around, but I think I can have maybe the best season of my career, and I’m motivated for that.”
Porte sits second in a tie-break with Impey, which is unlikely to change in the final flat stage of the race in downtown Adelaide on Sunday.
“Daryl is quick, he’s been second two times in the stages here against guys like [Peter] Sagan so realistically I don’t really have a chance to move up” he said.
“If I start going then Caleb Ewan and guys like this are going to go for the intermediates too. I’m happy with where I am all things considered.”