The US Open first introduced a tiebreak in the final set in 1970.
That year’s tournament became the first Grand Slam event to use a tiebreak to decide a set tied at 6–6, including the deciding set. The innovation was designed to prevent matches from continuing indefinitely and to give players, spectators and broadcasters a definite ending. The US Open initially used a sudden-death format in which the first player to reach five points won, provided the required margin was met under that system.
The experiment was controversial. Some players disliked the idea of allowing a short tiebreak to determine a match that might otherwise be settled through extended play. Nevertheless, the format quickly became an important part of modern tennis and influenced how other tournaments handled tied sets.
The US Open used its original best-of-nine-point sudden-death system from 1970 through 1974 before adopting the International Tennis Federation’s best-of-12-point format. Tiebreak rules have changed several times since then; from 2022, all four Grand Slam tournaments standardized an extended 10-point tiebreak at 6–6 in a final set.