World number 10 Casey began the day six under but picked up five shots on the front nine, narrowly missing with an eagle putt after driving the ninth green.
Hunter Mahan's tee shot on the 15th hole got stuck high up in a tree, leading to double bogey, but then he rolled in an eagle putt from off the 16th green.
Lingmerth finished a wild day with an 8-foot eagle putt on the par-5 16th and a 10-foot birdie on the island-green 17th to reach 12-under par when the third round was suspended because of darkness.
Els was the third player of the day to shoot 63, but his eight birdies and an eagle were offset when his five-wood approach splashed into the lake at the front of the green at the par-five 18th.