(comparative more hands down, superlative most hands down)
The origin of this colloquialism seems to have its roots in mid-19th century horseracing. When a horse jockey is nearing the finish line far ahead of the competition, "with victory certain", he could drop his hands, relaxing his hold on the reins, and still win the race. "By the late 19th century the phrase was being used in non-racing contexts to mean 'with no trouble at all.'"
See hand down