John Gill Commentary 2 Chronicles 28:5

"Wherefore Jehovah his God delivered him into the hand of the king of Syria; and they smote him, and carried away of his a great multitude of captives, and brought them to Damascus. And he was also delivered into the hand of the king of Israel, who smote him with a great slaughter." — 2 Chronicles 28:5 (ASV)

Wherefore the Lord his God delivered him into the hand of the
king of Syria
Whose name was Rezin, (2 Kings 16:5), though that is an after expedition to this, which is there related. The Lord is called the God of Ahaz, because he was so of right; he had dominion over him, and ought to have been worshipped by him; and, besides, he was so by virtue of the national covenant between God and the people Ahaz was king of; and moreover, Ahaz professed he was his God, though in an hypocritical manner, and he forsook the true worship of him.

and they smote him, and carried away a great multitude of them
captives, and brought them to Damascus ;
whereas in a later expedition, related in (2 Kings 16:5), they did not succeed.

and he was also delivered into the hand of the king of Israel ;
whose name was Pekah:

who smote him with a great slaughter ;
as is next related.