Dustin Johnson survived his biggest test of a long week in Austin as he edged into the final of the WGC-Dell Technologies Match Play.
Johnson was taken the distance for the first time in the tournament by the gallant Hideto Tanihara before a pivotal birdie at 17 and a clutch up-and-down at the last sealed a one-up win and a clash with Jon Rahm, who finished strongly to beat Bill Haas 3&2.
The world No 1, bidding to become the first player to win all four current World Golf Championship events, looked on course for another comfortable win when he holed a 35-foot putt for eagle at the sixth and then birdied the seventh to go three up.
But Tanihara fought back with birdies at the eighth and 10th, only to fall two behind again at the 12th when he raced his eagle putt five feet past the hole and missed the return.
However, Johnson then chunked a wedge at the next and Tanihara pitched to four feet and holed the chance, and he converted another excellent approach to six feet at the 14th to level the encounter.
Johnson again made a mess of a routine second into the 15th and lipped out for par, but he escaped with a half as Tanihara also failed to get up-and-down.
The top seed missed a good chance to regain the lead at 16, but he made light of his first visit to the 17th hole this week as he knocked his tee shot to six feet and rolled in the chance for a winning birdie.
Extra holes looked on the cards when Tanihara found the heart of the green at the last and Johnson's second spun back off the putting surface, from where he chipped to eight feet.
But Tanihara's 12th-foot putt to extend the contest slid past the target, and the rock-solid Johnson calmly found the centre of the cup to close out a tense victory that kept him on course for a third consecutive tournament victory.
Rahm had been in the clubhouse for 45 minutes by the time Johnson's match finished after the Spaniard enjoyed a late run of four birdies in five holes to see off Haas.
The pair won two holes each on the front nine and then traded pars and a birdie at 12 before Rahm pitched to six feet at the 13th and holed the chance to take the lead for the second time in the match.
Both got into trouble at the 14th and halved in bogeys, and Rahm clipped a delightful second in close at 15 following another mammoth drive to go two ahead with three to play.
Haas then missed the fairway at the long 16th and was unable to find the green in two, although he was given a lifeline when Rahm found the front-right bunker with his second.
But Haas played a poor chip and missed from 20 feet for birdie, and Rahm completed another big win when he splashed out to seven feet and drained the putt.