Jason Day's bid to defend his WGC-Cadillac Match Play Championship title got off to a losing start, while Rory McIlroy, Jordan Spieth, Sergio Garcia and Bubba Watson were among Wednesday's winners.
Australian Day lost to Charley Hoffman 4 and 3 in his first group-stage appearance at TPC Harding Park in San Francisco.
Day is spared an early exit, however, given the new format sees each of the 64 players in the field play three matches, with the best placed in each of the 16 groups advancing to the knockout stages.
However, Day and fellow 2014 finalist Victor Dubuisson have their work cut out for them after day one - with the Frenchman humbled 5 and 4 by Charl Schwartzel.
World number one Rory McIlroy won 5 and 4 over Jason Dufner, while Masters champion Spieth downed Mikko Ilonen 4 and 2.
Adam Scott's struggles continued, the former world number one going down 5 and 4 to Francesco Molinari.
Scott and Day joined fellow Australian Matt Jones as first-up losers, the latter edged 3 and 1 by Dustin Johnson, while John Senden (19 holes against 2007 champion Henrik Stenson) and Marc Leishman (3 and 2 over Justin Rose) flew the flag with wins.
There were 1-up wins for Brooks Koepka (over Russell Henley), Shane Lowry (over Graeme McDowell), Rickie Fowler (over Harris English), Lee Westwood (over Matt Every) and Jamie Donaldson (over Bernd Wiesberger).
Ben Martin also had a 1-up triumph over 2013 winner Matt Kuchar, benefitting from a hole-in-one on the 17th to gain the lead for the first time in the match on his luckless opponent.
Garcia was a 2-up victor over Tommy Fleetwood, as was Zach Johnson over Branden Grace.
Billy Horschel was a comfortable 5 and 4 winner over Brandt Snedeker, Ryan Moore trumped Danny Willett 3 and 2, and Bill Haas saw off Brendon Todd 3 and 2.
Champion in 2012, Hunter Mahan was the day's most convincing winner, exiting the course after just 12 holes with a 7 and 6 victory over Stephen Gallacher.
Ryan Palmer dismissed Anirban Lahiri 4 and 2, 2010 champion Ian Poulter won 3 and 2 over Webb Simpson and Patrick Reed got past Andy Sullivan 2 and 1.
Gary Woodland trailed through 15 holes, led after 17 but took until the 19th hole to beat Jimmy Walker.
Two-time Masters champion Watson thrashed Miguel Angel Jimenez 5 and 4, while Louis Oosthuizen was a convincing 6 and 5 winner against Keegan Bradley and Alexander Levy was no match for Hideki Matsuyama, who won their encounter 5 and 4.
Martin Kaymer beat Thongchai Jaidee 3 and 1, JB Holmes edged Marc Warren 2 and 1, Paul Casey defeated Chris Kirk after 22 holes while Kevin Na blew a two-up lead through 16 holes to fall to a 19-hole loss to Joost Luiten.