Scotland's Robert MacIntyre reached the last 16 of the WGC Matchplay - eliminating world number one Dustin Johnson in the process - by topping their group on a dramatic day in Texas.
England's Tommy Fleetwood survived a late scare to beat US Open champion Bryson DeChambeau and also progress.
Spain's Sergio Garcia landed a hole-in-one to beat England's Lee Westwood in a sudden-death play-off.
Northern Ireland's Rory McIlroy is out after a tie with Cameron Smith.
After beating McIlroy and Australia's Smith earlier this week, England's Ian Poulter won the group with a 100% record after another win against American Lanto Griffin.
The matchplay tournament at Austin Country Club sees the 64 players split into 16 groups of four, with only the group winners reaching the knockout stage.
'One of the best and luckiest shots I've hit in my life'
Few would have backed 24-year-old MacIntyre to reach the next stage after being drawn in the group containing Johnson - but the Scot progressed in remarkable fashion.
Needing to win the last in his final round-robin match against Adam Long, MacIntyre drove his tee shot within two feet of the hole on the par-four 18th and was given the eagle putt as he snatched top spot.
Seeded 41st in the 64-man event, MacIntyre clinched a half with a brilliant display against Johnson on Thursday - after being close to a shock win - to keep his hopes alive of progressing on Friday.
However, he looked to be going out when he was three down after nine holes against Long.
MacIntyre fought back after the turn and was one down going into the 370-yard last, with his inspired tee shot helping claim another important half.
That was enough to clinch top spot after Johnson lost to fellow American Kevin Na.
"I'm one down and need to win the hole, I played it last night and I had the same attitude: try to win the hole," said MacIntyre, who will play France's Victor Perez in the last 16.
"I hit probably one of the best and one of the luckiest golf shots I have hit in my life.
"It's massive for my confidence and massive going forward."
'I wanted both of us to go through' - Garcia beats Westwood with hole-in-one
England's Fleetwood had control of his own destiny after winning and halving his opening two matches, leaving him assured of progressing if he beat DeChambeau.
After being three up with five to play, Fleetwood lost the 14th to a birdie by the American and then three-putted on the 15th to see his lead cut to one.
Fleetwood would have faced a play-off with France's Antoine Rozner if he halved the match but, after a stray drive on the last, scrambled an unlikely par to secure a hard-fought victory.
Veteran European pair Garcia and Westwood needed a play-off to decide the winner of their closely-contested group - and it needed an extraordinary moment to separate them.
On their fourth extra hole, the Spaniard clinched his progress by holing his tee shot on the 161-yard par three.
"I hit a great nine iron and knew it was straight on line but I couldn't see because of the glare. When we heard the people cheer it was really nice," he said.
On pipping his good friend Westwood, he added: "It's tough because you want both of us to go through."
The 16 group winners go into Saturday's first knockout round, with the victors of each match progressing to the quarter-finals, which also take place on Saturday.
The semi-finals and final will be played on Sunday.
Round of 16 (all times GMT)
12:35 T Fleetwood (Eng) v D Frittelli (SA)
12:46 B Horschel (US) v K Streelman (US)
12:57 S Garcia (Spa) v M Hughes (Can)
13:08 R MacIntyre (Sco) v V Perez (Fra)
13:19 S Scheffler (US) v I Poulter (Eng)
13:30 J Rahm (Spa) v E van Royen (SA)
13:41 B Watson (US) v B Harman (US)
13:52 M Kuchar (US) v J Spieth (US)
- BBC Three brings you PRU: Four teens navigate the difficulties of adolescence in a school for excluded kids
- The End of Silence: Football's darkest secrets are uncovered