In this paper we model how the interaction of two species that compete for a common resource can be controlled by the introduction of a third species. This third species in the model can be considered as a bio-control agent. The aim here is to investigate whether the bio-control agent can slow, stall or even reverse the advance of one species into the territory of the other. We present conditions under which this can happen. The key point is that these conditions are on the relative strength of the bio-control agent. Thus, in application, these conditions could be met by choosing or designing the control agent appropriately and do not require the alteration of the properties of the existing species.