save someone's bacon

[A]n anxious eye had been kept on the pinnace and the vessel she was chasing. "She's up to her," cried Desmond, who was looking through his glass; "she struck without a blow, and there go our fellows tumbling on board. Little doubt, however, about her being a slaver, though, as they must have seen the way in which we got hold of this craft, they thought it as well to save their bacon, and make the best of a bad job."