1842, originally in dog racing, "dog that loses only the final race;" see runner + up. The more general sense of "team or competitor that takes second place" is from 1885.
Entries linking to runner-up
runner n.
c. 1300, "messenger on foot," agent noun from run (v.). The meaning "one who runs, a racer" is from early 14c.
With many technical senses. The meaning "smuggler, one who risks or evades dangers, impediments, or legal restrictions" is by 1721; the sense of "police officer" is from 1771. The botanical meaning "rooting stem of a plant" is from 1660s. The sense of "embroidered cloth for a table" is from 1888. In baseball, "a base-runner," by 1845.
up adv.
Old English up, uppe, from Proto-Germanic *upp- "up" (source also of Old Frisian, Old Saxon up "up, upward," Old Norse upp; Danish, Dutch op; Old High German uf, German auf "up"; Gothic iup "up, upward," uf "on, upon, under;" Old High German oba, German ob "over, above, on, upon"), from PIE root *upo "under," also "up from under," hence also "over."
As a preposition, "to a higher place" from c. 1500; also "along, through" (1510s), "toward" (1590s). Often used elliptically for go up, come up, rise up, etc. Up the river "in jail" first recorded 1891, originally in reference to Sing Sing, which is up the Hudson from New York City. To drive someone up the wall (1951) is from the notion of the behavior of lunatics or caged animals. Insulting retort up yours (scil. ass) is attested by late 19c.