<P> At the 1922 U.S. National Championships, the draw seeded players for the first time to prevent the leading players from playing each other in the early rounds . </P> <P> The open era began in 1968 when professional tennis players were allowed to compete for the first time at the Grand Slam tournament held at the West Side Tennis Club . The previous U.S. National Championships had been limited to amateur players . Except for mixed doubles, all events at the 1968 national tournament were open to professionals . That year, 96 men and 63 women entered, and prize money totaled US $100,000 . In 1970, the US Open became the first Grand Slam tournament to use a tiebreaker to decide a set that reached a 6--6 score in games . From 1970 through 1974, the US Open used a best - of - nine - point sudden - death tiebreaker before moving to the International Tennis Federation's (ITF) best - of - twelve points system . In 1973, the US Open became the first Grand Slam tournament to award equal prize money to men and women, with that year's singles champions, John Newcombe and Margaret Court, receiving US $25,000 each . Beginning in 1975, the tournament was played on clay courts instead of grass, and floodlights allowed matches to be played at night . </P> <P> In 1978, the tournament moved from the West Side Tennis Club to the larger and newly constructed USTA National Tennis Center in Flushing Meadows, Queens, three miles to the north . The tournament's court surface also switched from clay to hard . Jimmy Connors is the only individual to have won US Open singles titles on three surfaces (grass, clay, and hard), while Chris Evert is the only woman to win US Open singles titles on two surfaces (clay and hard). </P> <P> The US Open is the only Grand Slam tournament that has been played every year since its inception . </P>

Where was the us open tennis held before flushing meadows