Afterwards when he has chased the fight and the cry of battle from the ships, grant that he may return unharmed, with his armour and his comrades, fighters in close combat." Thus did he pray, and all-counselling Jove heard his prayer.

Part of it he did indeed vouchsafe him--but not the whole.

He granted that Patroclus should thrust back war and battle from the ships, but refused to let him come safely out of the fight.
When he had made his drink-offering and had thus prayed, Achilles went inside his tent and put back the cup into his chest.
Then he again came out, for he still loved to look upon the fierce fight that raged between the Trojans and Achaeans.
Meanwhile the armed band that was about Patroclus marched on till they sprang high in hope upon the Trojans.

They came swarming out like wasps whose nests are by the roadside, and whom silly children love to tease, whereon any one who happens to be passing may get stung--or again, if a wayfarer going along the road vexes them by accident, every wasp will come flying out in a fury to defend his little ones--even with such rage and courage did the Myrmidons swarm from their ships, and their cry of battle rose heavenwards.

Patroclus called out to his men at the top of his voice, "Myrmidons, followers of Achilles son of Peleus, be men my friends, fight with might and with main, that we may win glory for the son of Peleus, who is far the foremost man at the ships of the Argives--he, and his close fighting followers.