Chaudhary, seeded No. 2, defeated No. 7 Alex Lin of Gold River 7-6 (7), 6-4 in the boys 14s. The unseeded Nelson dominated No. 12 Ava Krug of Lakewood Ranch, Fla., 6-3, 6-1 in the girls 12s.
Chaudhary will face unseeded Martin Damm Jr. of Bradenton, Fla. Damm, whose father won the 2006 U.S. Open doubles title with Leander Paes of India and peaked at No. 5 in the world in doubles in 2007, downed No. 16 Timothy Li of Valley Village, Calif., 6-3, 6-4.
Chaudhary also advanced to the doubles final with Li. Seeded third, they will meet unseeded Damm and Aidan Mayo from Roseville.
Nelson will play No. 9 Violeta Martinez of Port Saint Lucie, Fla. Martinez edged No. 15 Alexis Blokhina of Fort Lauderdale, Fla., 6-3, 3-6 [10-8].
No. 8 Ryder Jackson of Nicasio and No. 16 Marcus McDaniel of Vacaville reached the round of 16 in the boys 16s, but Stevie Gould of Corte Madera and Cambell Nakayama of San Francisco lost.
Also, Jillian Taggart of Fair Oaks fell to No. 12 Eryn Cayetano of Corona, Calif., 6-4, 6-3 in the girls 16s.