Sydney - Leader Matt Jones complained of stinging eyes and trouble breathing as smoke from raging bushfires descended on the Australian Open for the second day running on Friday.
Jones birdied the final hole for a one-stroke lead over England's Paul Casey as the players struggled through another day of smoke haze.
World No 14 Casey, the highest-ranked player in the field, led for much of the day after a sparkling six-under-par 65.
But Jones, who won the tournament in 2015, sunk a tricky putt on the last to be 10-under for the tournament after his first-round 67.
Another Australian, Dimitrios Papadatos, was alongside Casey one shot back.
Five others, including South Africa's Louis Oosthuizen and Japanese amateur Takumi Kanaya, the joint overnight leader, were two behind Jones, who has won twice on the PGA Tour, but not since 2015.
A wind change helped lift some of the toxic smoke from bushfires blazing across New South Wales in the morning before beginning to return as the day wore on.
"As you can tell by the voice the smoke has got to me a little bit," croaked Jones.
"It's not the easiest to breathe, our eyes have definitely been stinging quite a bit.
"But any time you get to lead is fantastic. It would have been better to be more than one in front, but I'll take one."
World No 15 Adam Scott, who will be playing the Presidents Cup against Tiger Woods' US team next week, missed the cut despite firing a 67 as his first round of 75 cost him dearly.
His Presidents Cup International team skipper Ernie Els shot a 77 and will also miss the final two days, allowing him to focus on the task ahead next week at Royal Melbourne.
Former Masters champion Sergio Garcia was another to fall short of the cut.
Casey, who has won twice this year, at the PGA Tour's Valspar Championship and the European Open, said he was finally finding his range.
"I don't know if I was fully in the zone but it was really nice stuff and it felt really good," he said, after mixing seven birdies with a single bogey.
"Suddenly from a case of sort of bumbling around, just a couple under par, challenging for lead, so good stuff."
The 42-year-old added that he was in Sydney to win, as he targets the rare feat of wins on three different tours in a single season.
"Two victories this year, I'd love to have a third and that would be on three different tours, which would be pretty cool. I don't think I've done that before," he said.
"I'm not here to make up the numbers, I'm here to try and win."
Leading second round scores at the Australian Open at The Australian Golf Club in Sydney on Friday (par 71, AUS unless stated, *denotes amateur):
132 - Matt Jones 67-65
133 - Paul Casey (ENG) 68-65, Dimitrios Papadatos 67-66
134 - Louis Oosthuizen (RSA) 68-66, Cameron Tringle (USA) 69-65, Denzel Ieremia (NZL) 69-65, Shae Wools-Cobb, *Takumi Kanaya (JPN) 65-69
135 - *Yu Chun-an (TPE) 65-70, Scott Arnold 68-67, *Lukas Michel 68-67
136 - Mark Brown (NZL) 71-65, Ben Eccles 68-68, Brett Rumford 69-67, Marc Leishman 69-67, Blake Windred 68-68, *Hayden Hopewell 68-68
137 - Deyen Lawson 72-65, *Elvis Smylie 70-67, Fraser MacLachlan (NZL) 69-68, David Bransdon, Wade Ormsby 68-69, Aaron Pike 71-66
138 - Ryan Chisnall (NZL) 71-67, David Micheluzzi 70-68, Abraham Ancer (MEX) 72-66, Stephen Allan 70-68, Peter Lonard 69-69. Andrew Martin 69-69
139 - Greg Chalmers 71-68, Ryan Fox (NZL) 71-68, Nathan Green 70-69, Rod Pampling 69-70, Justin Warren 72-67, *Louis Dobbelaar 72-67, Aaron Wilkin 71-68, Michael Hendry (NZL) 70-69, Richard Green 72-67, Jason Scrivener 68-71, Michael Wright 73-66
140 - KJ Choi (KOR) 69-71
142 - Adam Scott 75-67
143 - Mike Weir (CAN) 75-68
144 - Sergio Garcia (ESP) 70-74
149 - Ernie Els (RSA) 72-77