At a blow

Also found in: Idioms.
suddenly; at one effort; by a single vigorous act.

See also: Blow

References in classic literature ?
At length, obliged to beat a retreat before superior numbers, they formed an intrenchment behind the large table, which they raised by main force; whilst the two others, arming themselves each with a trestle, and using it like a great sledge-hammer, knocked down at a blow eight sailors upon whose heads they had brought their monstrous catapult in play.