The Open Era began in 1968 when all five events were merged into the newly named U.S. Open at the West Side Tennis Club in Forest Hills, Queens. Notably, the 1968 combined tournament was opened to professionals; neither predecessor tournament allowed professionals to compete
. That year, 96 men and 63 women entered the event with prize money amounting to $100,000. The US Open was originally played on grass until Forest Hills switched to hard courts in the mid '70s. In 1978, the event moved from Forest Hills to its current home at Flushing Meadows.
ก็น่าจะเป็นประมาณความเห็นข้างบน คือเปิดกว้าง เพราะก่อนหน้านั้นมีการจำกัดหลายๆอย่าง