World number one Jason Day says he is "running on empty" as he prepares to defend his US PGA Championship crown.
The Australian has played just one practice round on Baltusrol’s Lower Course after spending Tuesday night in hospital with his wife, who had an allergic reaction.
Day, 28, could lose his number one spot if he finishes 29th or worse and Dustin Johnson is in the top two.
“I'm just a little bit under the weather,” said Day, who is playing a third consecutive week for a rare time on his schedule.
“I've got to really try and manage my patience out there, because I have very little patience right now. For some reason, every time I get a little bit under the weather, I've got zero patience.”
Day, whose magical run to the summit of world golf gathered steam when he won his first major at Whistling Straits last year, looked clear atop the rankings in early June.
But with Dustin Johnson similarly breaking through for his first major championship at the US Open and subsequently throwing down a series of great results, the worm has turned.
Day enters this week with only two scenarios that could dethrone him from the No.1 ranking – if Johnson wins and he can’t finish at least tied second, or if Johnson is solo second and he can’t be 28th or better.
At the majors since his win last August, the Queenslander has finished tied 10th in the Masters, tied ninth in the US Open and tied 22nd at The Open.
“It's very, very difficult to win golf tournaments,” he said.
“I think everyone expects if you're in the lead, or if you're a favourite to win, you will win, and if you don't, then you're in a slump. It's not the case.”
And the rankings race is close enough to potentially put Day off his game – or encourage his best game.
“It is added motivation for sure. Obviously I want to keep the world No.1 spot, but I can't focus on it too much,” Day said.
“The biggest thing for me is to focus on what I need to do to play well.
“I can't attach myself to the thought of keeping it, I have to focus on trying to prepare the best I can and execute and play well.”
Day was delighted with his closing 67 at last week’s Canadian Open where he couldn’t defend his crown, but made huge inroads after his flat Open Championship at Troon a week earlier.
A string of late birdies as he came to grips with North American greens again made all the difference to his confidence and mindset before his first major title defence.
“I know it is going to be really hot so I need to slowly ease my way into it after the last two days in Canada were confidence building.”
Day leads a nine-strong Australian tilt with Adam Scott, Aaron Baddeley, Greg Chalmers, Marcus Fraser, Scott Hend, Matt Jones, Marc Leishman and John Senden also in the field for the year’s final major championship.
Tee times for Rd1:
7:00 AM (9.00 PM AEST) Bradley Dredge Patton Kizzire Mark R. Brown
7:10 AM K.J. Choi Tommy Sharp Jon Curran
7:20 AM Jason Kokrak Josh Speight Kristoffer Broberg
7:30 AM Darren Clarke David Lingmerth Daniel Berger
7:40 AM Aaron Baddeley Kevin Kisner Emiliano Grillo
7:50 AM John Daly Padraig Harrington Vijay Singh
8:00 AM Victor Dubuisson Marcus Fraser James Hahn
8:10 AM Soren Kjeldsen Billy Hurley III Scott Hend
8:20 AM Matt Jones Rikard Karlberg Charley Hoffman
8:30 AM Robert Streb Vaughn Taylor Kevin Na
8:40 AM Gregory Bourdy Jonas Blixt Roberto Castro
8:50 AM Ross Fisher Omar Uresti Greg Chalmers
9:00 AM Zac Blair Smylie Kaufman David Muttitt
12:15 PM Joe Summerhays Yuta Ikeda Colt Knost
12:25 PM Ryan Palmer Rob Labritz Gary Woodland
12:35 PM Alex Noren Andrew Johnston Scott Piercy
12:45 PM Shaun Micheel Rich Berberian Jr. Rocco Mediate
12:55 PM Tony Finau Anirban Lahiri Matthew Fitzpatrick
1:05 PM (3.05 PM AEST) Danny Lee Matt Kuchar Luke Donald
1:15 PM Jim Furyk Francesco Molinari Shane Lowry
1:25 PM Bubba Watson Jordan Spieth Sergio Garcia
1:35 PM Patrick Reed Justin Rose Charl Schwartzel
1:45 PM Danny Willett Dustin Johnson Henrik Stenson
1:55 PM Graeme McDowell Webb Simpson Louis Oosthuizen
2:05 PM Ryan Moore Kyle Reifers Ben Polland
2:15 PM Mitch Lowe Kevin Streelman Young-han Song
7:00 AM Chris Kirk Wyatt Worthington II Freddie Jacobson
7:10 AM Jason Bohn Jeunghun Wang Brian Gaffney
7:20 AM J.B. Holmes Brian Stuard Hideki Matsuyama
7:30 AM Tyrrell Hatton Harris English Matt Dobyns
7:40 AM Rickie Fowler Ernie Els Zach Johnson
7:50 AM Chris Wood Branden Grace Jimmy Walker
8:00 AM Justin Thomas Rafa Cabrera-Bello Paul Casey
8:10 AM Brooks Koepka Brandt Snedeker Lee Westwood
8:20 AM Adam Scott Keegan Bradley Jamie Donaldson
8:30 AM Jason Day Phil Mickelson Rory McIlroy
8:40 AM Bill Haas Jamie Lovemark Andy Sullivan
8:50 AM George Coetzee Rod Perry Hideto Tanihara
9:00 AM Nicolas Colsaerts Ryan Helminen
12:15 PM Michael Block Harold Varner III John Senden
12:25 PM Kevin Chappell Johan Kok Troy Merritt
12:35 PM Russell Henley Fabian Gomez Thorbjorn Olesen
12:45 PM Rich Beem Steve Stricker David Toms
12:55 PM James Morrison Brandon Stone Billy Horschel
1:05 PM Jason Dufner Martin Kaymer Y.E. Yang
1:15 PM Bernd Wiesberger Byeong Hun An Brendan Steele
1:25 PM Marc Leishman Kiradech Aphibarnrat Russell Knox
1:35 PM Jim Herman Thongchai Jaidee Thomas Pieters
1:45 PM Soomin Lee William McGirt Joost Luiten
1:55 PM Brad Lardon K.T. Kim Peter Malnati
2:05 PM Daniel Summerhays Cameron Tringale Rick Schuller
2:15 PM Brad Ott Bryce Molder Si Woo Kim