Rory McIlroy could be excused if he didn't know where he stood in his match against Smylie Kaufman. He was 1 up and 1 down over the opening four holes. The lead changed nine times until McIlroy pulled ahead and closed out Kaufman on the 17th hole in the Dell Match Play.

That earned him another victory, and something that isn't easy to find at Austin Country Club.

Clarity.

McIlroy faced Kevin Na on Friday to close out round-robin play, and it's as simple as it gets. The winner advances from his group to the round of 16. The loser goes home. The knockout stage essentially starts one day early.

"There's no doubt in your mind," McIlroy said. "You win your match and you're playing on Saturday morning or you're going home. And in that way, it's nice because you can go out on the golf course and not have to look at the other match in your group. 'Oh, if he does this, maybe I don't have to win.' So there's clarity in your mind.

"You go out and you try to win and that's it."

If only it was that simple for the other 10 groups.

Math was required through the world ranking to determine the 64-man field. More math is required to figure out who is going to advance.

Jordan Spieth and Jason Day were among four players who have the best chances to move on. Even if they lose their match, they are at least assured of a sudden-death playoff because there are no tiebreakers this year.

But there are three groups in which every player can wind up in four-man playoff. In one of those groups, all four players are 1-1 going into Friday.

Real clarity begins in the round of 16, when the single-elimination begins.

THE EASY ROAD: Spieth had another stress-free match in beating Victor Dubuisson of France, 5 and 4. Day recovered from his back injury — his tee shot on the 381-yard opening hole that was 12 feet from the cup was a good indication — and hammered Thongchai Jaidee.

Brooks Koepka and Rafa Cabrera-Bello also are 2-0 in their groups. That means they only need a halve in Friday's matches to move on.

HEAD-TO-HEAD: The All-American match on Friday is Phil Mickelson and Patrick Reed, one of four matches in which it is winner-take all. The others are McIlroy against Kevin Na, Matt Kuchar against Justin Rose, and Louis Oosthuizen against Andy Sullivan.

Mickelson was the only one who was seriously challenged.

He was all square with Daniel Berger on the 18th hole when Berger drove left in front of a rock wall of the 10th tee. He hit the rock with his swing on the way down, the club missed the ball and he let it go, grabbing his left wrist. Berger looked over at Mickelson and conceded the match.

Rose and Kuchar were challenged, though it ultimately didn't matter. Each halved their matches — Rose against Anirban Lahiri, Kuchar against Fabian Gomez. Because Lahiri and Gomez lost their opening matches, neither can win their group. That means the winner of Rose-Kuchar advances.

ALMOST HEAD-TO-HEAD: Two other matches are nearly winner-take-all, except that halves are involved. Adam Scott plays Bill Haas in one group, and Charl Schwartzel plays Brandt Snedeker in the other. Yes, the winner advances. However, Scott gave up a late lead Wednesday and halved his match. Snedeker gave up a late lead Thursday and halved his. That means if Haas and Schwartzel play to a draw, both advance.

THE COMPLICATED: Three groups have scenarios in which all four players can wind up in a sudden-death playoff. That includes the group with Rickie Fowler, who is happy to still have even a remote chance. Scott Piercy narrowly missed a 10-foot putt on the 18th hole to beat Fowler, which would have sent Fowler and his high-tops packing.

Patton Kizzire birdied the 18th for a halve, putting him in the same predicament as Fowler (but in a different group).

And then there's Group 8: Dustin Johnson, Jimmy Walker, Robert Streb and Kiradech Aphibarnrat. All of them are 1-1 going into Friday.

MASTERS NO LONGER ON THEIR MINDS: Of the 22 players mathematically eliminated Thursday, five were outside the top 50 in the world ranking and cannot move up and qualify for the Masters: Jaco Van Zyl, Thomas Pieters, Matt Jones, Thorbjorn Olesen and Marcus Fraser.

The cutoff for the top 50 who get to Augusta National is this week.