sentences:  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.From 1975, following complaints about the surface and its impact on the ball's bounce the tournament played on clay courts instead of grass, this was also an experiment to make it more "TV friendly".