The Dubliner, 50, shot a second round 66 to sit just one off the lead being set by Scott Dunlap at Warwick Hills Golf and Country Club.
The longest hitter on the tour, Harrington birdied three of the four par fives on the layout in a bogey-free round. [How much could McIlroy win? Padraig Harrington is just one shot off the lead going into the final round of the Ally Challenge as he seeks his second win in two weeks.