Both Choi and Webb turned in bogey-free rounds and are one stroke up on Min Lee, Mika Miyazato and Yoo Sun-young, who each had two bogeys in their 5-under 66s.
Han Hee-won and Park Hee-young are tied for sixth at 4-under with seven other players are at 3-under.
Choi had birdies on each even-numbered hole on the front side and added birdies at Nos. 12 and 14 on the second nine
Webb's round featured three birdies on each side and included birdies on the two par 3s -- Nos. 15 and 17 -- on the second nine.
The LPGA Malaysia tournament is the first stop of a four-tournament Asia swing. The tour heads to South Korea next week and also has events scheduled in Taiwan and Japan.