yadyapy astraṁ brahma-śiras tv amoghaṁ cāpratikriyam vaiṣṇavaṁ teja āsādya samaśāmyad bhṛgūdvaha
Translation
Oh Sounaka the glory of the family of Bhrigu, although the Supreme weapon of the Brahma released by Aswathama was irresistible and without any check or counteraction, still when it was confronted with the strength of Vishnu (Lord Krishna) the same became neutralised and foiled.
Purport
In the Bhagwat Geeta it is said that Brahmayoti or the glowing effulgence transcendental is resting on Lord Shri Krishna. In other words the glowing effulgence known as Brahma Teja is nothing but rays of the Lord as much as the sun rays are to the sun disc. So this Brahma weapon also, although materially it is irresistible without any check still the Lord being Supreme nothing could surpass His strength. The weapon of the name Brahmasiras released by Aswathama was neutralised and foiled by Lord Shri Krishna by His own energy that is to say He did not wait for any other's help in any case because He is Absolute.