Miyazato, who won the event in 2010, had five birdies in a six-hole stretch of the second nine in moving to 14-under 202 after 54 holes. Yani Tseng last year's winner in Thailand, had a second consecutive 65 and is second at 13-under.
Webb owned a three-stroke lead after Saturday's completion of the weather-delayed second round and Miyazato still trailed by three after a 2-under front nine. She tied for the lead with back-to-back birdies at Nos. 10 and 11 and moved in front with three straight birdies over 13-15.
Tseng was tied for the lead with Miyazato and Webb after nine holes Saturday but fell back to Miyazato's hot streak. She pulled close with a birdie at the 18th.