All alone; without any assistance.

Saying that one could beat an opponent single-handedly is not the same thing as saying that he/she could do it 'with one hand tied behind his/her back'. That saying means that the upcoming fight or task will be very easy.
Sal (a guy) carried everyone's bags up the hill single-handedly.
by Diggity Monkeez May 22, 2005
Get the Single-Handedly mug.