World number one and WGC-Cadillac Match Play top seed Rory McIlroy has been drawn in a difficult group with three Americans at this week's tournament at TPC Harding Park in San Francisco.
The tournament has a new format this year, with 16 groups of four and one winner from each group advancing to the knockout stages after the round-robin games between Wednesday and Friday.
Group two contains recent Masters winner Jordan Spieth and Lee Westwood, while elsewhere Bubba Watson has been drawn in a heavyweight group four with Louis Oosthuizen, Keegan Bradley and Miguel Angel Jimenez.
WGC-Cadillac Match Play groups
Group 1: Rory McIlroy, Billy Horschel, Brandt Snedeker, Jason Dufner
Group 2: Jordan Spieth, Lee Westwood, Matt Every, Mikko Ilonen
Group 3: Henrik Stenson, Bill Haas, Brendon Todd, John Senden
Group 4: Bubba Watson, Louis Oosthuizen, Keegan Bradley, Miguel Angel Jimenez
Group 5: Jim Furyk, Martin Kaymer, Thongchai Jaidee, George Coetzee
Group 6: Justin Rose, Ryan Palmer, Anirban Lahiri, Marc Leishman
Group 7: Jason Day, Zach Johnson, Branden Grace, Charley Hoffman
Group 8: Dustin Johnson, Victor Dubuisson, Charl Schwartzel, Matt Jones
Group 9: Adam Scott, Chris Kirk, Paul Casey, Francesco Molinari
Group 10: Sergio Garcia, Jamie Donaldson, Bernd Wiesberger, Tommy Fleetwood
Group 11: Jimmy Walker, Ian Poulter, Webb Simpson, Gary Woodland
Group 12: J.B. Holmes, Brooks Koepka, Russell Henley, Marc Warren
Group 13: Rickie Fowler, Graeme McDowell, Shane Lowry, Harris English
Group 14: Matt Kuchar, Hunter Mahan, Stephen Gallacher, Ben Martin
Group 15: Patrick Reed, Ryan Moore, Danny Willett, Andy Sullivan
Group 16: Hideki Matsuyama, Kevin Na, Joost Luiten, Alexander Levy