Ian Poulter staged a superb comeback to beat Rory Sabbatini on the 18th and reach the quarter-finals at the WGC-Accenture Match Play.
Poulter is the only remaining European in the event after Luke Donald and Sergio Garcia lost in the third round.
The Englishman was two down with five to play and said: "That was a fairly gutsy finish."
Poulter will face Nick O'Hern, who followed his second-round win over Tiger Woods with victory over Donald.
O'Hern is one of three Australians in the quarter-finals.
Adam Scott saw off Garcia 4&3 while Robert Allenby ended Kirk Triplett's hopes.
Phil Mickelson's bid for a third successive US Tour win was thwarted by his regular Ryder Cup partner David Toms.
Friday's surprising results mean that only two of the top 10 seeds are still in contention.
"That's the beauty of this tournament," said Toms.
"[Phil Mickelson] and I were talking, when he shot that low round at Spyglass [in the Pebble Beach National Pro-Am], you get a big lead on the field.
"Here, you can do that in one match. And the next match, if you don't play well you're gone."
US Open champion Retief Goosen is the highest seed left in the competition at four. The South African rallied from three down with eight holes to play to beat Chad Campbell on the 19th hole.
Quarter-final tee-off times
All times GMT, seedings in brackets
1530: (16) Chris DiMarco (USA) v (8) Stewart Cink (USA)
1540: (4) Retief Goosen (Rsa) v (44) Robert Allenby (Aus)
1550: (31) Nick O'Hern (Aus) v (42) Ian Poulter (Gbr)
1600: (14) David Toms (USA) v (11) Adam Scott (Aus)