Rory McIlroy extended his unbeaten streak at the WGC-Dell Match Play to 11 matches to move into the quarter-finals at Austin Country Club.
The defending champion came into the last 16 clash against Zach Johnson with 2.5 points from the group stages but he had been made to work for it, needing 55 holes to get past Thorbjørn Olesen, Smylie Kaufman and Kevin Na.
His opponent by contrast, had needed just 42 holes to canter to victory in Group 14 and had looked like the form man of the week in Texas coming into the knockout stages.
The World Number 15 could not find that level of performance on Saturday morning, but he pushed McIlroy all the way again, with the four-time Major Championship winner eventually prevailing by one hole.
"I would have liked to play better, but I played a little bit better than Zach and that's what I needed to do," he said. "I made some birdies but made a few mistakes.
I'm just happy to be through to the quarter-finals and hopefully the standard of my golf can go up another level this afternoon - Rory McIlroy
"I've got to convert a little bit better. I missed a couple of putts, I gave away two or three really soft holes. You can't do that. You can't do that in match play, especially at this stage.
"I need to play the par threes a little better, as well. My par three playing hasn't been great this week.
"I've been a little conservative with my lines. At this stage of the game you need to be aggressive. I'm going to go out and fire at pins and make as many birdies as I can."
McIlroy got off to a poor start, with a chip shot advancing less than two feet as he conceded the first, but Johnson missed from inside five feet to drop the second and a brilliant McIlroy approach saw him win the next.
Another poor chip from the Northern Irishman allowed Johnson to take the fourth before the next three holes were shared but, when the American found a bunker with his second shot on the eighth, a par was enough to move McIlroy ahead.
A three-putt bogey on the tenth from the World Number Three levelled matters again but he could have won the next two but for a 36-foot birdie putt and an excellent par save after finding the water from Johnson.
McIlroy was ahead on the 13th as Johnson failed to get up-and-down and the lead was extended on the 15th as he found a bunker off the tee for two bogeys in three holes.
But the Open Championship winner is made of stern stuff, and when he put his approach on the 16th to eight feet, a birdie closed the gap to a single hole.
Chris Kirk is next up for McIlroy after the American beat countryman Bill Haas 2 and 1.
World Number Two Jason Day is also into the last eight after a 3 and 2 win over Brandt Snedeker and he will next face Brooks Koepka, who beat 2013 champion Matt Kuchar by one hole.
