Billy Horschel, Matt Kuchar, Scottie Scheffler and Victor Perez are all vying for a spot in the WGC-Dell Technologies Match Play final after a day of upsets in Austin.
Stars Jon Rahm, Tommy Fleetwood and Sergio Garcia surprisingly crashed out in the quarter-finals as the underdogs ruled on Saturday.
The unpredictable tournament continued on the weekend after world number one Dustin Johnson, Justin Thomas, four-time major winner Rory McIlroy, U.S. Open champion Bryson DeChambeau and Patrick Reed were unable to advance beyond the group stage.
Spanish third seed Rahm topped Erik van Rooyen 3 and 2 in the last 16 before being upstaged by Scheffler 3 and 1 in the quarter-finals at the Austin Country Club.
"I felt like I played some really good golf," said Scheffler, who will meet Kuchar in an all-American clash for a spot in Sunday's decider. "I think I kept things bogey-free and I got some early leads and made sure that I kept the pressure on those guys and made them feel like they had to do something special to beat me, which they weren't able to do."
Fleetwood – the 21st seed – succumbed to Horschel after 19 holes, while former Masters champion Garcia was beaten by 31st seed Victor Perez 4 and 3.
American golfer Horschel and France's Perez will do battle in the semis.
Englishman Fleetwood was sent packing after hitting a hole-in-one during his last-16 victory – a drive out of bounds at the 12th seeding him come unstuck in the quarters.
It was a big day for 2013 champion Kuchar, who eliminated former world number one Jordan Spieth 1up before defeating Brian Harman 2 and 1.
Kuchar – the 52nd seed – was runner-up in 2019, with last year's event cancelled due to the coronavirus pandemic.
"Certainly golf's a funny game and I think there are times as a professional where you can feel so far away, you think, golly, I don't have it," Kuchar said.
"I'm racking my brain trying to find it, but then you plug in the right ingredient, the right key, and then all of a sudden it snaps back, and thankfully it's been working and I'm seeing progression. It's just finally now it's clicked and it's a lot more fun this way, I assure you."