Julieta Granada, the winner of the 2004 U.S. Girls' Junior Championship, finished one shot back at minus-6 after closing with a 2-under 68. Linda Ishii posted a 4-under 66 to take third place at 5-under-par 205.
Kim Brozer, last week's winner, led a group of players tied for fourth at minus-4.
Granada climbed one clear of Reno until the 14th. Granada's drive went well left into the trees and she struggled to a triple-bogey to drop two behind Reno.
Reno, one of five leaders after two rounds, rolled in a 20-foot birdie putt on the 15th to extend that lead to three. Granada got one back with a birdie on 16 and Reno's lead was one after she tripped to a bogey on 17.
The 25-year-old Reno got up and down for par from over the 18th green for the win.
'I kind of knew this morning it was going to be a good day and after the ninth hole, I felt like I was going to win,' said Reno. 'I just felt it today, and I wasn't going to let anything get to me.'
Brozer was joined in fourth place at 4-under-par 206 by Clarissa Childs, Seon-Hwa Lee, Charlotte Mayorkas and Sun Young Yoo. Allison Hanna and Nicole Castrale, a two-time winner this season, were one stroke further back at minus-3.