The 23-year-old double major winner is the headline act at the Royal Sydney Golf Club along with Adam Scott.
The 23-year-old double major winner hasn't played since last month's Ryder Cup and is the headline act at the Royal Sydney Golf Club along with local favourite and world number seven Adam Scott.
"I feel renewed. I feel mentally in a good place right now going into the end of this year and next year," said Spieth, who is currently ranked fifth.
"I've had some tremendous time off, been able to feel like I'm completely rested, get to do some things in the swing that I've been trying to work on for a year now."
The American is chasing his second Australian Open title in three years.
A final round 63 propelled him to a six-shot victory in 2014 and his title defence last year fell one shot short when he and Scott were joint runners-up behind Australian Matt Jones, who is not defending his crown this week.
Spieth has two worldwide victories in 2016 and has been unable to recapture his remarkable form from 2015 when he won five times on the US PGA Tour including back-to-back majors at the US Masters and US Open.
"I wanted to come back here," he said. "This tournament is very important. It was a springboard two years ago."
Spieth is searching for his first victory since May and tees off early Thursday alongside former US Open winner Geoff Ogilvy and reigning US Amateur and Asia-Pacific Amateur champion Curtis Luck.
Ogilvy is fresh off a tie for fourth two weeks ago at the US PGA Tour's Shriners Hospitals for Children Open in Las Vegas and is confident he can add to his Australian Open win in 2010.
"I feel capable of playing better than I ever have," the 39-year-old Australian said.
"Whether that actually eventuates for scores or not, I don't know, but I feel like I know my game better than I ever have. Golf-wise I feel better than I ever have."
Scott -- the 2009 Australian Open champion -- will headline the Thursday afternoon field when he tees off alongside Venezuelan Jhonattan Vegas and fellow Aussie Aaron Baddeley.
The 2013 Masters champion returns to Royal Sydney for the first time since his memorable duel three years ago with Rory McIlroy when the Northern Irishman birdied the 72nd hole to defeat Scott by one shot.
Scott is vying for his first victory since back-to-back wins on the US PGA Tour in February and March.
Veteran Rod Pampling is also in the field, fresh from his first US PGA Tour title in more than a decade at the Shriners Open.
The top three players in Sydney will win direct entry into next July's British Open at Royal Birkdale.