Definition of lucky loser in English:

lucky loser

noun

Sport
  • 1(Chiefly Tennis) a competitor who loses in the qualifying round of a competition, but is given a place in the main draw after the withdrawal of another player through injury, illness, etc.

  • 2A competitor, team, etc., who is not placed highly enough to qualify automatically for the later stages of a competition, but who gains entry by being one of the best-placed losers, or by playing a further knockout round.

Origin

1950s; earliest use found in Mirror (Perth).