Senior, the 43-year-old who resides in Queensland, followed up a first-round 68 with a 6-under par round that has him heading into the weekend holding a one shot advantage over New South Wales' Paul Sheehan.
Sheehan has posted rounds of 69-66 for a two-day total of 9-under-par 135.
Two more Queenslanders are two off the pace and includes the first-round leader Grady. Grady shot a 2-under-par 70 to lose the lead but remains into contention as they head to the weekend.
Alongside Grady is Shane Tait, who put together rounds of 69 and 67 and sits with Grady at 8-under for the tournament.