Rory McIlroy produced his best performance of the week so far to beat Chris Kirk 4 and 3 and move into the semi-finals of the WGC-Dell Match Play.
The defending champion had not had it all his own way so far at Austin Country Club, needing 55 holes to get out of the group stage and then being taken down the last by Zach Johnson in the last 16 before claiming a one hole win.
The World Number Three had still managed to extend his unbeaten run at this event to 11 matches, however, and that became 12 as four birdies in six holes on the back nine saw off the challenge of Kirk, who had been level at the turn.
He is now just two wins from becoming only the second man to defend this title, following in the footsteps of Tiger Woods who won in 2003 and 2004 at La Costa Resort & Spa.
"It's been a long week," he said. "I played 55 holes in three days coming into today, and then to go all the way with Zach, it was nice to get a couple of holes off.
"I played very well this afternoon. I think it's the best I've played all week, and obviously the score reflects that.
"I feel like each and every day I've improved a little bit.
"I think I made six or seven birdies out there this afternoon. I made a couple of mistakes and gave a couple of holes away, but for the most part I was very pleased with how I played.
Even if tomorrow doesn't quite go the way I want it to, I feel like I've still made a lot of great strides forward this week - Rory McIlroy
McIlroy hit a wonderful approach and made an 11-footer to move ahead with a birdie on the first and, when Kirk got in trouble on the fourth after putting his tee-shot over the green, the lead was two holes.
A wayward tee-shot from McIlroy led to the Northern Irishman taking a drop and Kirk capitalised with a birdie to reduce the gap, before a missed short putt resulted in a McIlroy bogey on the ninth and things were level at the turn.
An approach to six feet allowed McIlroy to bounce straight back and win the tenth and he then overcame a ragged tee-shot on the par five 12th to birdie again and move two up.
The 26 year old drove through the green at the 13th and when Kirk put his second in the water, another birdie and a three hole lead was to follow, before an approach to six feet saw off Kirk on the 15th.
Jason Day awaits in the semi-finals after the Australian moved back to Number One in the Official World Golf Ranking with a 3 and 2 win over Brooks Koepka.
Day put his approach to the third to seven feet to go one up but he missed a four-footer on the fifth to allow Koepka to get back on level terms with an excellent birdie.
Koepka moved ahead with another on the next but Day levelled things up once more with the help of a 13-foot putt on the eighth.
An approach to eight feet resulted in a Day birdie on the tenth before an eagle led to a concession from Koepka and a two-hole lead on the 12th.
The 28 year old had his irons tuned in and a pitch to three feet on the par five 15th sealed a fourth birdie of the match.
