In the boy's division, Chris DeForest of Cottekill, N.Y., shot a 4-under 67 at Westfield Country Club to move to 13-under 200, breaking the 54-hole record of 202 set by Pat Perez in 1993.
The 12-year-old Thompson, from Coral Springs, Fla., who missed the cut in the Open at Pine Needles last month, had four birdies on the back nine to pull into a tie with Kim, a 15-year-old from Pahoa, Hawaii.
Cassandra Blaney, a 17-year-old from Davenport, Fla., eagled the par-5 10th and is a shot back in third after a 3-under 68.
The 18-year-old DeForest has only two bogeys through 54 holes and leads Mark Johnson of Tulsa, Okla., by six shots. Connor Driscoll of Encinitas, Calif., and Luke Guthrie of Quincy, Ill., are 10 shots back in third.
The Junior PGA Championship is one of the premier junior championships of the summer. It features 156 boys and girls who are 18 or under and have not started college. Past champions include David Toms, Trevor Immelman, Sean O'Hair, Cristie Kerr and Grace Park.
It was one of the few junior events not won by Tiger Woods, who finished second to Chris Couch in 1990.
Copyright 2007 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.