single-handedly

Single-handedly means entirely without anybody else's help. One person, and the whole job.

It is nearly always admiring, so single-handedly saving a business or single-handedly organising an event gives full credit to one person, and it is a generous thing to say. It can be ironic, since single-handedly ruining an evening is also possible. The image comes from sailing, where single-handed means crewing a boat alone, and single-handed round-the-world races are a real and serious thing.