Apollo encouraged Ares to take Diomedes out of the combat.  Ares in the form of Akamas stiffened the Trojan fight for the wounded double of Aineias. 

Sapedon fired by Ares chided Hektor for cowardliness.  Hektor, shamed, leaped from his chariot and rallied the Trojans.  Ares seeing that Athena had left the field cloaked the Trojans in a dusk.  Apollo sent the healed Aineias with his courage restored into battle.  A brutal clash erupted and the Greeks strengthened their ranks with reserves.

Diomedes using the clear vision given to him by Athena saw that Ares lead the Trojan onslaught.  He withdrew fighting so that the Trojans could not break the Greek lines.