Divide And Conquer.

The collision created an explosion of thunder and light. The world was rocked, and mortals stumbled as they ran about to hide. 

All of these appeared within the sight of the Celestial Supreme, and it pleased her. Demons can invade this plane easily since it doesn't have a divine plane, but that doesn't mean she, the Celestial Supreme, will stand and watch it happen.

The portal was bombarded by her intent, empowered by her Authority and world power. It shook and flickered. Its runes began to scatter, and the spatial tunnel it was opening began to collapse. 

Destruction is easier than creation, and destruction is easiest with lightning, so it was not surprising that the portal began to collapse.

The collapse of the portal was further hastened as a terrible sound came from the other side of it. 

"Rawr"