Austin - World number four Jordan Spieth and seventh-ranked Rory McIlroy were ousted from the World Golf Championships Match Play Championship on Friday with defeats in final group matches.
US 18th seed Brian Harman never trailed in dispatching McIlroy 5&3 and capturing his group with two wins and a draw.
Spieth was knocked out by US Ryder Cup partner Patrick Reed, who won their much anticipated match 2&1.
Reed, ranked 23rd in the world, never trailed and rolled in a 40-foot putt from off the 17th green to end Spieth's hopes of a first title of 2018.
Both will now try to regroup with the first major of the year, the Masters, two weeks away.
Sergio Garcia, tuning up for his Masters title defence at Augusta National, rallied from 2 down through 11 holes to beat rising US star Xander Schauffele 3&1 and reach the last 16.
"Xander played unbelievable on the front nine, tricky conditions, and he kept making good putt after good putt on me," Garcia said. "So I was just hoping to stay in it and give myself some chances as soon as he gave me a little opening on 12.
"And then I was able to make a great birdie on 13, 15 and 16," added Garcia, who next faces American Kyle Stanley.
Thomas pummelled Italian Francesco Molinari 7&5 to set up a meeting with South Korean Kim Si-woo - a 2 up winner over Webb Simpson.
The only thing Thomas could find to regret was that the match only lasted through 13 holes.
"Today I'd be really excited to see how low I could go," said Thomas, who will take on Kim in the round of 16. "I could post a serious number."
McIlroy, managed only two birdies in his final competitive tuneup for the Masters, the only major title the Northern Ireland star needs to complete a career Grand Slam.
"Rory did not play his best golf today but I played extremely well," said Harman, a two-time winner on the US PGA Tour.
"I'm proud of the way I came out. Rory is an intimidating guy. He hits it a mile. I had this one (match) circled this week and I'm glad I came out and performed pretty well," added Harman, who set up a meeting with two-time Masters winner Bubba Watson.
Watson birdied the last two holes to halve his match with 64th-seeded Julian Suri.
McIlroy, coming off a victory at Bay Hill last Sunday, admitted he was feeling weary.
"That takes it out of you being in contention, and all that mental energy," he said.
Other top players who didn't make it past group play included world number one and defending champion Dustin Johnson, former world number one Jason Day, five-time major winner Phil Mickelson and Spain's Jon Rahm.
South Africa's Louis Oosthuizen beat Day 2 up, then won his group in a playoff against Jason Dufner with a par at the first hole.
American Charles Howell rolled unbeaten to his group crown by downing Japan's Satoshi Kodaira 2&1.
That eliminated Mickelson, seeded 18th, who had kept his hopes alive by edging Spain's Rafa Cabrera Bello 1 up.
Thailand's 28th-seeded Kiradech Aphibarnrat booked a last-16 clash with Howell with a 4&3 victory over third seed Rahm, who had already been eliminated and finished the week winless.
Results from Friday's final group-stage matches at the World Golf Championships Dell Match-Play Championship at Austin, Texas (x denotes seed):
Kevin Kisner (USA x32) bt Dustin Johnson (USA x1) 4&3
Adam Hadwin (CAN x38) and Bernd Wiesberger (AUT x52) halved
Justin Thomas (USA x2) bt Francesco Molinari (ITA x21) 7&5
Patton Kizzire (USA x48) bt Luke List (USA x60) 4&2
Kiradech Aphibarnrat (THA x28) bt Jon Rahm (ESP x3) 4&3
Chez Reavie (USA x43) and Keegan Bradley (USA x63) halved
Patrick Reed (USA x19) bt Jordan Spieth (USA x4) 2&1
Charl Schwartzel (RSA x49) bt Li Hao Tong (CHN x34) 3&2
Patrick Cantlay (USA x30) bt Hideki Matsuyama (JPN x5) 4&3
Cameron Smith (AUS x46) and Yusaku Miyazato (JPN x53) halved
Brian Harman (USA x18) bt Rory McIlroy (NIR x6) 5&3
Peter Uihlein (USA x57) bt Jhonattan Vegas (VEN x44) 4&3
Sergio Garcia (ESP x7) bt Xander Schauffele (USA x20) 3&1
Dylan Frittelli (RSA x41) bt Shubhankar Sharma (IND x62) 1 up
Jason Dufner (USA x42) bt James Hahn (USA x56) 3&2
Louis Oosthuizen (RSA x25) bt Jason Day (AUS x8) 2 up
(Oosthuizen wins group over Dufner with par on first playoff hole)
Tommy Fleetwood (ENG x9) bt Daniel Berger (USA x26) 2&1
Ian Poulter (ENG x58) bt Kevin Chappell (USA x33) concession, back injury
Matthew Fitzpatrick (ENG x31) bt Paul Casey (ENG x10) 3&2
Kyle Stanley (USA x45) bt Russell Henley (USA x51) 1 up
(Stanley wins group over Casey with birdie on second playoff hole)
Bubba Watson (USA x35) and Julian Suri (USA x64) halved
Marc Leishman (USA x11) and Branden Grace (RSA x23) halved
Charley Hoffman (USA x22) bt Tyrrell Hatton (ENG x12) 3&2
Brendan Steele (USA x36) bt Alexander Levy (FRA x55) 3&1
(Hatton wins group over Steele with birdie on first playoff hole)
Alex Noren (SWE x13) bt Tony Finau (USA x29) 1 up
Thomas Pieters (BEL x39) and Kevin Na (USA x61) halved
Phil Mickelson (USA x14) bt Rafa Cabrera Bello (ESP x17) 1 up
Charles Howell (USA x59) bt Satoshi Kodaira (JPN x40) 2&1
Kim Si-woo (KOR x50) bt Webb Simpson (USA x37) 2 up
Gary Woodland (USA x24) bt Pat Perez (USA x15) 1 up
Matt Kuchar (USA x16) bt Ross Fisher (ENG x27) 6&4
Yuta Ikeda (JPN x47) and Zach Johnson (USA x54) halved