The 20-year-old Kim, from Del Mar, Calif., beat Robby Shelton IV of Wilmer, Ala., 1 up in the morning quarterfinals, and topped Eric Sugimoto of San Diego 4 and 3 in the afternoon semifinals.
"I didn't make any bogeys in the afternoon round," said Kim, the low amateur in the U.S. Open at Merion after winning the Jack Nicklaus and Fred Haskins awards as the college player of the year. "If you do that, you're going to be tough to beat."
The 19-year-old Niebrugge, from Mequon, Wis., edged 16-year-old Dou Zecheng of China 1 up in the quarterfinals, and beat James Erkenbeck of San Diego 3 and 2 in the semifinals.
"Today was tough," Niebrugge said. "Thirty-six (holes) today (meant) your legs were getting tired, so you had some errant shots, but I just reminded myself about posture and started hitting it a little better. Overall, I played great."
The tournament is limited to players who don't hold privileges at any course that doesn't extend playing privileges to the general public. The winner of the 36-hole final traditionally receives a spot in the Masters, if still an amateur.
"It would mean a lot," Kim said. "I look around at the banners that are up of previous winners—Trevor Immelman, Brandt Snedeker, Tim Clark.
Kim, set to play in the Walker Cup matches, is No. 2 in the world amateur ranking.
"I think I'm playing well enough to stay with anybody right now," Niebrugge said. "I've been under par every match. If I keep doing that, I'll keep the match close. That's the main goal: Keep it close and you never know what can happen."
The temperature reached 98 degrees.
"We usually complain whenever the wind picks up because the course plays harder," Kim said. "But the last few days, we were so happy when it was blowing so we could stay a little cooler."
Niebrugge fought to stay hydrated.
"It was tough to stay cool out there," Niebrugge said. "I drank about 30 waters today."