World No. 1 Dustin Johnson stayed on track to become the first player to win all four World Golf Championships events, when he advanced to the semi-finals at the WGC-Dell Matchplay in Texas on Saturday.
Johnson will face Japan's Hideto Tanihara in the semi-finals after the 54th seed beat England's Ross Fisher 4&2.
"If I end up playing against Dustin, I might benefit not looking at what he's doing because he's such a great player", said Rahm.
"In theory I shouldn't even be here - one chip has gotten me here", Haas said.
The Northern Irishman did not hold the lead at any point during the match-up, although he managed to level the scores with two holes to play.
Schwartzel birdied the first hole to seize the lead over Casey, but the Englishman squared the match with a par at the fourth and never trailed again.
We've all been there, lining up the flawless tee shot, practice swing looking good, visualising the ball landing in the middle of the fairway...only to see the ball veer off into the water or the bushes or roll two feet away from the tee.
"There's a lot more strategy and thinking in playing this kind of format", said Tanihara, a 14-time Japan Tour victor in his WGC Match Play debut who hopes to crack the world top 50 and qualify for the Masters in two weeks.
Johnson was almost flawless during pool play and cruised past Zach Johnson, 6 and 4, in the Round of 16.
Mickelson had three birdies on his round while Leishman, the victor last week at the Arnold Palmer Invitational, conceded three holes after poor shots left him out of position. Rahm sent Kjeldsen, one of the hottest players in the field, packing with a dominant 7 and 5 victory. He was 2-down through 15 and had a chance to cut the margin on 16, but missed an eagle putt that would have won the hole.
"That putt on 13 I think was a big one, " Johnson said.
Haas had to survive a six-hole, sudden-death playoff with No. 64 K.T Kim of South Korea on Friday in which he had to chip in for par on the second hole and then had to par the final hole in the Saturday's round of 16 to outlast No. 46 Kevin Na. It took him just four tournaments to earn his PGA tour card, and 12 events to earn his first victory in the Farmers Insurance Open at Torrey Pines. "Hopefully I can keep it going tomorrow".
Rahm, who won his first PGA title in January at Torrey Pines, would be the youngest victor of any WGC event, breaking the mark Patrick Reed who was 23 when he won at Doral in 2014.