Jason Day says he'll have to fight to keep pace with a "fearless" pack of young leaders at the US PGA Tour's Memorial Tournament that includes a teenaged former amateur star.
The former world No.1, whose poor record at Memorial includes just one top-25 from nine appearances, sits three shots off the pace courtesy of a 68 which has left him at four under.
Posting his best opening round in two years at his hometown event in Columbus, Ohio, Day still trails 19-year-old Joaquin Niemann from Chile as well as unheralded Mexican Abraham Ancer and Japanese ace Hideki Matsuyama.
The trio fired a seven-under-par 65 at Muirfield Village to take a one-shot lead over American Beau Hossler (66) going into day two of the Jack Nicklaus-hosted tournament.
"It's been a while since I gave myself a good opportunity to contend here," Day said.
The 30-year-old admits it will take a hot second round to reel in Niemann, a former world No.1 amateur who Day says isn't lacking in confidence.
"These guys are so young but they're coming out with a boatload of confidence," Day said.
"They're not scared to shoot low numbers or play against the best players in the world.
"You've just got to keep working hard to try and stay ahead."
World No.8 Day, who has two US Tour wins already this year, said a fever which forced his withdrawal from Wednesday's pro am reared its head on Thursday.
"I had a fever on Sunday and I lost 10 pounds (4.5kg)," Day said.
"With the heat today, I was a little bit shaky because you're just not used to such a quick weight change."
Day sits four shots ahead of fellow Australians Adam Scott and Cameron Davis, who along with Tiger Woods (all 72) sit at even par.
Five-time Memorial champion Woods delighted the Muirfield Village galleries when he rallied back from a nightmare score which blew out to four over during his front nine, which he attributed to back soreness.
"My back is fused; I'm going to have days where it's just tight," Woods said.
"I didn't feel my swing and consequently I hit it both ways but I fought back."
Rod Pampling and John Senden (73), Marc Leishman (74) and Cameron Smith (75) round out the Australian contingent.