Liam Doran put Isa ahead only for Steve Hughes to level on the hour.
Fellow title aspirants Sychdyn also dropped points, being held 1-1 at home by lowly Mostyn Dragons.
Mark Weir's 45th minute penalty was not enough for the villagers as Ralph Butterley equalised on 75 minutes to salvage the visitors a share of the spoils.
Offa Athletic are up to fourth following a 2-1 verdict at Aston Park Rangers, Matthew Bennett (2) for the visitors, Alec Sumner for the host team.
In the Horace Wynne Cup semi-finals, gap Connah's Quay beat Flint Mountain 4-0.
Cefn Mawr Rangers entertain Acton in the other semi on Thursday.