• McIlroy lies one shot behind former winner Chalmers• Adam Scott roars back into contention with round of 66Greg Chalmers has a one-shot lead at the halfway stage of the Australian Open on Friday but defending champion Rory McIlroy is well-positioned for the weekend in a share of second place.Chalmers, twice a former winner of his national open, snared his seventh birdie on the last green for a five-under-par 66 to edge ahead of a congested leading pack at five-under for the tournament.