In what year did the US Open introduce the tiebreak? The answer is 1970.
The US Open became the first Grand Slam tournament to use a tiebreak, adopting the rule when a set reached 6–6 in games. Its original format was different from today’s: the first player to reach five points won, and a 4–4 score created a sudden-death finish. The rule was used in both singles and doubles.
The innovation was associated with Jimmy Van Alen, whose tiebreak concepts were designed to prevent marathon sets from stretching matches indefinitely. Players initially disliked the change, while spectators appreciated having a clear finish line. The 1970 US Open men's final included a tiebreak, with Ken Rosewall defeating Tony Roche.
A common mix-up concerns the format rather than the year. The US Open introduced its original nine-point tiebreak in 1970; the familiar seven-point tiebreak format was introduced there in 1975. From 1970 through 2018, the US Open was also the only major where singles matches could end with a final-set tiebreak.