Lee had four birdies on the back nine and another three on the front to take the lead from Lang.
''Everything felt good today, the driver, the 6-iron, the putter ... they were all good,'' the 24-year-old Lee said. ''My goal was 3-under par every day this week, so I feel like I'm OK for the next couple of days.''
Lang started off on the back nine with four straight birdies and was set to share the lead with Lee before a bogey on her final hole.
''I played great, didn't make too many mistakes, hitting the ball fantastically and had a lot of tap-in birdies,'' Lang said. ''But I didn't finish off as strong as I'd like to. It gets pretty hot towards the end, so I need to get some rest and just make sure I'm eating and drinking enough out there.''
Park also said the 90-degree weather made it difficult.
''I think I was affected a lot by the hot weather, that really made it hard to concentrate on the course,'' Park said. ''I'm not a good player to play in such condition. But I've had success in recent years, like this year in Thailand and last year here in Malaysia. So I'm trying to relax a bit more and keep it going tomorrow.''