All three players completed 36 holes of stroke play at four-under-par 138, and Moll, of Houston, Texas, drew the No.1 seed in match play. The 18-year-old won the first two holes against Josh Bartels of Lincoln, Neb., on Wednesday and went on to a 5-and-3 victory. Moll, who is competing in his first USGA championship, hit his approach shot on the par-4 10th hole to eight feet and drained the putt to kick-start a streak of three straight winning holes that sealed his win.

“It was really awesome; it was like a whole new experience playing singles match play,” said Moll, who will attend Vanderbilt University in the fall. “You only have to beat one guy. You can adjust your play off how they play.”

“You only have to beat one guy. You can adjust your play off how they play.” – William Moll

Castillo, 18, of Yorba Linda, Calif., earned a spot in the Round of 32 for the third consecutive year by escaping with a 1-up victory over Drew Salyers. The No.2 seed, Castillo relinquished a 4-up lead to Salyers before rebounding to take the lead back with a conceded par on No.17. Castillo clinched his win with a seven-foot par putt on the 18th hole.

“Played a little sloppy, had a little pressure on me, but in the end it worked out,” Castillo said. “Hopefully I can keep it going tomorrow.”

One of the top performances of the day came from Mouw, the No.3 seed, who defeated Jake Beber-Frankel, 6 and 4. Mouw, 18, of Chino, Calif., had the shot of the day on the par-4 11th, which was playing at 261 yards, when he hit a 3-iron to within a foot of the hole for a conceded eagle and a 4-up lead. At No.20, Mouw is the second-highest ranked player in this week’s field in the World Amateur Golf Ranking (WAGR).

The biggest upset of the day came from Sean Curran, the No.58 seed. Curran, of New Lenox, Ill., survived an 8-for-7 playoff on Wednesday morning by sinking a 20-foot birdie putt, then defeated No.7 seed Brett Roberts, 2 and 1. No.55 seed Yuki Moriyama, of Japan, defeated No.10 Karl Vilips, of Australia, 4 and 2. Vilips is No.53 in the WAGR, sixth-best position in the field.

- United States Golf Association