The dapper Englishman, mining a rich vein of form since leading Europe to Ryder Cup victory over the United States in September, notched six birdies in perfect conditions at Kingston Heath Golf Club in Melbourne to be among three tied for second at five-under, including local favourite Adam Scott.
"Five-under was a decent day but I feel like this golf course, if you play really well, can lend itself to making plenty of birdies, especially in these conditions," 36-year-old Poulter said.
"I think with my game, I'd prefer it to be a little windier than what it was today. I play pretty well in the wind and this is a tricky golf course."
Poulter stormed to victory by three strokes in last year's tournament at nearby Victoria Golf Club on Melbourne's famed sandbelt, blitzing local challengers who crumbled in gale-force winds in the final round.
The world number 16 is less likely to get his wish for Friday's second round, when teeing off in the relative calm of the morning.
While Poulter and Scott compete for top billing at the A$1 million tournament, journeyman Guyatt upstaged them both with a sparkling 65, featuring eight birdies and a single bogey.
"I've never been in this position before," said Queenslander Guyatt, who returned to play the fledgling OneAsia tour this year after a five-year hiatus working at a Brisbane golf club.
"It's what you do all your hard work and your practice for."
World number five Scott battled early frustrations on the greens before finding his putting groove to be well placed to bid for his first victory of the year.
"Realistically, I felt 9 or 10 (under) was possible for the way I played today if everything went my way," he said. "I'm not complaining, it's a good start."
Scott was joined in his group by Northern Irishman and former Major winner Graeme McDowell, who carded a 71 to be six shots adrift of Guyatt.
1 Matthew Guyatt -7
T2 Adam Scott -5
T2 Ian Poulter -5
T2 Michael Hendry -5
T5 Kalem Richardson -4
T5 Craig Hancock -4
T5 Rika Batibasaga -4
T5 Peter O'Malley -4
T5 Jake Higginbottom-4
T5 Paul Gow -4
T11 Rohan Blizard -3
T11 Mahal Pearce -3
T11 Brody Ninyette -3
T14 Cameron Smith -2
T14 Chris Campbell -2
T14 Michael Foster -2
T14 Alex Hawley -2
T14 Craig Scott -2
T14 Jared Pender -2
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- Kingston Heath Golf Club
- Adam Scott