The pair finished 54 holes knotted at 11-under-par 205.
Haas is trying to become the second generation of his family to take the Houston event -- his father Jay won it in 1987 -- and will seek his fifth career title against Cink, who is looking for career win No. 7.
His last win was the 2009 British Open.
Falling into a third-place tie at minus-10 was second-round leader Steve Wheatcroft, who bogeyed the last hole en route to and even-par 72.
Ben Crane (67), first-round leader D.A. Points (71) and Jason Kokrak (71) joined him in third on the Tournament Course at Redstone Golf Club.