AUSTIN, Texas -- Dustin Johnson answered a rare challenge and Jon Rahm delivered another early knockout Saturday to advance to the semifinals of the WGC-Dell Technologies Match Play, staying on track for a potential showdown between No. 1 in the world and golf's brightest new star.
Johnson has looked so unbeatable this week that he led all 71 holes he had played until he lost a 3-up lead at the turn and was all square in his quarterfinal match when Alex Noren of Sweden holed a 40-foot birdie putt on No. 12.
Johnson answered with three birdies in four holes and won 3 and 2.
Rahm was so dominant Saturday he played only 27 holes in two matches, and none of his past three matches have gone beyond the 14th hole. The 22-year-old rookie from Spain still hasn't played the 18th hole since a practice round Tuesday.
After a 6-and-4 victory over Charles Howell III in the morning fourth round, he was even better in a 7-and-5 victory over Soren Kjeldsen. Rahm said only his 65 in the final round to win at Torrey Pines was a better brand of golf.
"The golf I've played the last three matches really has been very impressive, even to myself," he said. "And it seemed to get better as I played, which is something that doesn't happen often."
Rahm faces a semifinal match Sunday morning against Bill Haas, who ended Phil Mickelson's hopes with a 2-and-1 victory in the quarterfinals. Mickelson had advanced to the quarters for the first time in 13 years with a victory against Marc Leishman.
Mickelson never trailed in any match until he fell behind on the first hole to Haas, and he never led when the match ended on the 17th hole.
"I struggled making the putts that I have been making all week," Mickelson said. "That seemed to me to be the difference."
Johnson, going after a third straight PGA Tour title, faces one of this tournament's biggest surprises in Hideko Tanihara of Japan.
Tanihara began the week by beating Jordan Spieth. On Saturday, he took down Paul Casey with two late birdies in the morning, and then beat Ross Fisher 4 and 2 to reach the semifinals.
"He looks unbeatable," Tanihara said. "I hope he doesn't feel good tomorrow, so maybe I have a chance."
Johnson has looked unstoppable all month.
He went to No. 1 in the world with a five-shot victory at Riviera. In his next start, he won the Mexico Championship after holding off a late rally from Rahm. Now he's two victories away from becoming the first player to sweep the four World Golf Championships.
None of Johnson's five matches has gone beyond the 16th hole. In the fourth round, he beat Zach Johnson 5 and 4. Noren is the only player to really make him sweat, and that was Johnson's doing.
Johnson went 3 up at the turn, and then it was gone. He three-putted from 30 feet to lose the 10th hole. His tee shot on the par-3 11th hit the rocks and went into the water. And then he had to settle for par after leaving himself in an awkward spot, only to watch Noren hole a 40-footer to tie the match.
Johnson holed a 10-foot birdie putt on the 13th -- Noren missed from 8 feet -- and then began to pull away with another 10-foot birdie on the 15th.
"That putt on 13, I think, was a big one," Johnson said. "That was just outside of him, and to hole that putt, put a little pressure on him, and then he missed it, I think that was a pretty important shot there."
Haas is still amazed to even be playing. On Friday, he was on the verge of being eliminated when he hit into a hazard in a sudden-death playoff against K.T. Kim to decide their group. Haas took a penalty drop, chipped in from 120 feet for par to halve the hole and won on the sixth extra hole. Then he had to go 18 holes to beat Kevin Na in the fourth round before taking on Mickelson.
Haas made seven birdies in his match. He figured he will need something close to that number for his semifinal match against Rahm.
Fisher left with a consolation prize. The Englishman finished with three straight birdies in Mexico that enabled him to qualify for this 64-man field, made another birdie in a playoff to advance out of group play and then defeated Bubba Watson in the fourth round Saturday morning. Even though he lost in the quarterfinals, Fisher will move into the top 50 in the world ranking next week and qualify for the Masters.
Tanihara also was assured of being in the top 50 to get into Augusta National for the first time in 10 years.
"My whole goal starting the year was to get into the Masters," he said.