Kim stood at 10-under 200 after 54 holes and put him in position to claim his fourth PGA Tour title.
Only one stroke behind was Scott Stallings, who fired a 4-under 66 to finish at minus-9.
Simpson managed a 1-under 69, dropping into a share of third at 8-under-par 202 with Gary Woodland (67).
De Jonge, meanwhile, fell to a 2-over 72, tumbling into a tie for 11th at 5-under 205.
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