NeSmith, 18, won the Class AAAA individual golf title at Furman University Golf Club.
The senior opened the 54-hole tournament Monday with a pair of 3-under-par 69s to open up a five-shot lead.
He finished with 70 to finish at 8-under 208, which was good for an eight-shot triumph over his closest competitor. His winning total is the third best in the history of the tournament, which dates to 1939.
In the team competition, South Aiken shot 922 and finished third as Easley (897) rallied to win the title by 11 shots over Blythewood.
North Augusta tied for 10th place with 948.
The Thoroughbreds of South Aiken were led by Hayden Ploeger and Ryan Carpenter, who tied for seventh place at 223. Both earned all-state honors.
One of the top junior players in the country, NeSmith has played in the first two Junior Invitationals at Sage Valley events and has won multiple junior tournaments around the country.
NeSmith, who is committed to play at South Carolina, also will be honored this week at the HP Byron Nelson Championship in Irving, Texas.
He is one of four junior golfers who will receive the Byron Nelson International Junior Golf Award, which recognizes players from around the world for their accomplishments on the course and in their community.