You have a few options. Consider, for example, that the Universe is a nigh-endless landscape. Whole space fleets could get lost in certain situations.
Maybe just have one such fleet - a colonial fleet, thus light on weapons - of the Not-Race find themselves jumping through hyperspace and dropping out due to some bizarre pulsar nonsense.
So a) wrecks their technology/communications, b) breaks their ships doomed to crash-land mostly, c) renders the Not-Race scattered, disorganized, and without viable supplies, weapons, and so forth.
Now, they could definitely fall back to some good old melee weapons, and they might have SOME advanced weaponry that simply doesn't have supplies to continue (and they without adequate machinery to resupply), etc.
Leaving the Not-Race to go into straight triage mode and survival tactics. You'd have some larger ships crashing/landing with suitable hosts to bring the pain to local Human populations, but in many others it's going to be some freaky terrifying stuff for both sides.
All sort of depends on what sort of Not-Race you're looking for.
But yeah, it's definitely easy to even the odds.