From the middle of the 18th fairway, Jo made a clutch shot. With a berth in the final on the line, her 120-yard approach stopped 5 feet short of the hole.
''That shot, I didn't think I would hit it that close,'' said Jo, a ninth-grader at the Xiwai International School in Shanghai. ''My mom's a good caddie, so she told me to relax. I couldn't have made it without her.''
Ha two-putted for par after her approach rolled long to the back of the green, and Jo's short birdie tap gave her the victory.
''She just outplayed me (on 18),'' said Ha, who will attend Vanderbilt in the fall.
Seong twice earned 1-up advantages over Uriell through the first nine holes. But Uriell, an incoming freshman at the University of Arkansas, never let Seong run away with the match.
''My opponent did really well putting, so that was the pressure,'' said Seong, who is trying to become the first stroke-play medalist to win the championship since Candie Kung in 2001.
Jo or Seong will become the second-youngest champion in WAPL history. Jo and Seong are both younger than Yani Tseng was when she won in 2004 at age 15. Michelle Wie was 13 when she won in 2003.
The championship is scheduled to conclude with a 36-hole final on Saturday.