Moira Dunn took third place at 4-under-par 68. Patricia Meunier-Lebouc, Gloria Park, Brandie Burton and Giulia Sergas tied for fourth place at 3-under-par 69.
Han started on the back side at Bosque Real Country Club and jumped out of the gate with a birdie at the par-4 10th. She then birdied three in a row starting at the par-3 14th and added a 7-foot birdie at the par-5 18th to make the turn at 5 under.
The 26-year-old kept on rolling on the front nine with a birdie at the par-4 first. Han then birdied the par-4 third to reach 7 under par but found trouble with a bogey at the par-3 seventh. She parred her two remaining holes to secure a one-shot edge over Jo.
'The course is in great shape and we had really nice weather,' said Han, a three-time winner on the LPGA Tour. 'I hit my irons pretty good and my putting was almost perfect.'
Jo ran off seven straight pars before she picked up her first birdie of the day at the par-4 eighth.
The 20-year-old from South Korea caught fire on the inward half with a birdie at the par-three 11th and another at the par-4 13th. Jo then birdied the 16th and closed with a birdie at the last to finish within one of the lead.
Annika Sorenstam was back in action this week and the Swede tallied her first birdie at the 12th, her third hole of the day. Sorenstam added a birdie at the 17th to move to minus-2 around the turn but gave that shot back with a bogey at the par-4 fourth.
Sorenstam recovered with a birdie at the very next hole en route to a round of 70.
'I thought I played some good golf today and hit some good shots,' said Sorenstam. 'I am really happy with my start.'
She was joined by Carin Koch, Cristie Kerr, Michelle Estill and Sae-Hee Son at 2 under par.
Local favorite Lorena Ochoa was one shot further back in a group at 1-under-par 71.