The 19-year-old Cal junior was in a tie for third and two shots off the lead after making birdies at 10, 12, 13 and 15.
The San Diego resident, who came to America with his family from South Korea when he was 7 years old, imagined for a moment winning the U.S. Open. The trophy was in his hands and people were cheering "Go Bears!"
Then he hit a horrible drive at the 16th hole that led to a bogey. Then after hitting his tee shot into the greenside bunker at the 254-yard par 3 17th, he made a sloppy double-bogey that he followed with a bogey at the 18th.
Still his 1-over 71 was a remarkable round of golf on a very difficult course that yielded a 74.356 stroke average in the third round. If Kim can hold on to his tie for 10th after Sunday's final round, he would be the first amateur to get a top-10 at the Open since Jim Simons finished in a tie for fifth at Merion in 1971.
An amateur hasn't won this championship since Johnny Goodman took the '33 Open at the North Shore Country Club, outside Chicago.
Kim, who qualified through the sectional qualifier at the Hawks Ridge Golf Club in Ball Ground, Ga., won four college events this year and took the Jack Nicklaus Award for the top college golfer. But teenagers aren't supposed to contend on a brutally hard course like Merion. They don't dream that big.
"I didn't really know what to expect coming in, honestly. Just wanted to make the cut," Kim said. "I thought that would be a pretty good week.
"I didn't feel that nervous, but I definitely think I was, looking back on it. And just a few loose swings and a couple bad putts and it is what it is."
Van Pelt was impressed with the wiry kid who grew up playing at the Torrey Pines Golf Course.
"[Kim] didn't look like he was surprised that he was playing good," Van Pelt said. "He didn't hit many drives off line. He hit everything solid and he's a really good putter. He doesn't overpower the golf course, but he's long enough.
"He had a tough finish but those closing holes are really hard. There are certain tournaments where you dog a guy for finishing bogey, double-bogey, bogey, but at this place you don't have to hit a shot very bad to have some bad holes."
Kim has been helped a lot this week by his caddie, LaRue Temple, who has worked at Merion for the past 16 years. Temple showed his young boss the right lines off several tees and assisted him with reading putts.
"For probably the first 12 holes today, LaRue was getting more cheers than I was," Kim said. "Everybody was going 'LaRue! LaRue!' "
In the previous three U.S. Opens, an amateur has finished in the top 21. Last year, before he turned pro, Jordan Spieth had a tie for 21st at the Olympic Club. Kim is one of four amateurs to make the cut at Merion, including his Cal teammate Michael Weaver, who shot 78 in the third round.
Kim said he believes that a course like Merion gives every player a chance to compete, regardless of age or experience in major championships.
"On this course, anybody who puts it in the fairway has a good chance out here, and I've done a pretty good job of that," he said. "But it's definitely gotten better and better each year and these guys in college are pretty good, and I think it's great that we get a chance out here to prove it."
On Sunday, Kim will have an opportunity to do what no amateur has done in 42 years. In '71, Jim Simons was a 21-year-old Wake Forest senior when he held the 54-hole lead at Merion after shooting a 65 in the third round.
Paired with Jack Nicklaus in the final round, he held the lead with nine holes to play. A birdie at the 72nd hole would have gotten him into a playoff with eventual winner Lee Trevino and Nicklaus. Instead, he ended up in a tie for fifth.
Kim didn't know who Simons was when he was asked about him on Saturday. But the All-American has a chance to join Simons, who died in 2005, in the history books.
On Sunday, Kim will be paired with Rickie Fowler, someone who knows all about being a young player in the limelight. As a 21-year-old rookie, Fowler played in the 2010 Ryder Cup. Through Fowler, Kim can see what his life will be like in a few short years.