PERTH, Australia, Oct 18, 2012 (AFP) - Dufner's effort around the par-72 layout left the world No.10 six strokes off first-round leaders, New Zealand's Michael Hendry and Spain's Alejandro Canizares.
Hendry and Canizares both opened with seven-under 65.
"I got off to a nice start," Dufner said. "But I didn't really finish it off. Thought I was going to put a good score on the board after 12 holes.
"But I just couldn't make the par saves that I needed to.
"I've got a long way to go to get back up towards the lead, but the good thing is there's three days left."
Schwartzel, the 2011 US Masters Champion, was also disappointed with his opening round.
"I got off to a really good start. But I found it very difficult to judge the wind on this golf course," Schwartzel said.
"It feels very inconsistent, so it was hard to pull the right club.
"But one-under is what it is. I really feel like I can shoot a low score out there. So just stay patient and see."
The South African is confident he can make up the leeway.
"Six shots is nothing. There's so many holes to go. It's just a start. You can lose it in the first round but you can't win it in the first round."
Paul Casey also stormed into contention with a 67 in the trickier, windy afternoon conditions.
"I'm really happy with a 67. I gave myself lots of birdie chances," said the Englishman, who was No.3 in the world behind Tiger Woods and Phil Mickelson two years ago.
But he has slipped to the 130s in the rankings after dislocating a shoulder in a snowboard accident on Christmas Eve last year.
Canizares, ranked 246, made a late decision to come to Perth after missing the cut in Portugal last week.
The Australian event, co-sanctioned by the European and Australasian PGA tours, is just one of two events left this season for him to bolster his world ranking.
"A win here would solve the problem," said the Spaniard.
New Zealander Hendry, ranked 574, has won three times in his own country and spent most of his time playing at home. He intends to try to qualify on the Japanese Tour for 2013.
He is coached by New Zealand Institute of Sport's Craig Dixon, who also mentors teenage sensation Lydia Koh.
Australian Greg Chalmers, the defending Australian Open and PGA Championship winner, shot a solid round of four-under 68 to be three shots off the pace.
And in an ominous warning to his rivals, the world No.58 said he was confident he will improve during the tournament as he gets used to the conditions.
"Look, two days ago I was in Dallas, Texas," Chalmers said.
"I made a couple of soft bogeys just purely out of my brain feeling a little like a mashed potato."
Scores after the opening round of the $Aus2 million ($2.04 million) EPGA-sanctioned Perth International at Lake Karrinyup (par-72) in Perth on Thursday (Australia unless stated):
65 - Michael Hendry (NZL), Alejandro Canizares (ESP)
66 - Emiliano Grillo (ARG)
67 - Andrew Johnston (ENG), Paul Casey (ENG)
68 - Ashley Hall, Max McCardle, Jason Scrivener, Rhys Davies (WAL), Greg Chalmers, Andrew Dodt
69 - Carlos Del Moral (ESP)
70 - Thomas Petersson (SWE), Richard Bland (ENG), Daniel Fox, Brad Lamb, Matthew Guyatt, Alastair Forsyth (SCO), Andre Stolz, Knut Borsheim (NOR), Jin Jeong (KOR), Jamie Moul (ENG), Heath Reed, Craig Lee (SCO), Markus Brier (AUT), Bo Van Pelt (USA), Jason Norris, Leigh Deagan
71 - Edouard Dubois (FRA), Terry Pilkadaris, Steve Jones, Charl Schwartzel (RSA), Jason Dufner (USA), Edoardo Molinari (ITA), Scott Strange, Anthony Summers, Matthew Millar, Scott Laycock, Aaron Townsend, Peter Wilson, Ian Esson, Rick Kulacz, Mark Brown (NZL), Robert Coles (ENG), David Howell (ENG), Federico Colombo (ITA)
Selected scores:
72 - Steve Webster (ENG), Thomas Norret (DEN), Scott Jamieson (SCO), Lorenzo Gagli (ITA), Sam Little (ENG), Andy Sullivan (ENG), Andrea Pavan (ITA)
73 - Oliver Wilson (ENG), Gary Boyd (ENG)
74 - Matthew Baldwin (ENG), Ignacio Garrido (ESP)
75 - Daniel Denison (ENG), Mikael Lundberg (SWE), Tommy Fleetwood (ENG)
76 - James Kingston (RSA)
77 - Mikko Ilonen (FIN), Gareth Maybin (NIR), Oscar Floren (SWE), George Murray (SCO), Johan Edfors (SWE), Peter Hedblom (SWE),
78 - Joakim Lagergren (SWE), Jose Lara (ESP)