This summer, thanks to the advent of the Open era in 1968, the US Open will celebrate its 50th anniversary.
Prior to the inaugural US Open, played in Forest Hills, only amateurs were permitted to play in Grand Slam tournaments and other events sanctioned by the International Lawn Tennis Federation, now known as the ITF.
In that era, New York's Grand Slam was known as the U.S. National Championships, and being an amateur tournament, prize money was not on offer.
But in 1968, beginning with the French Open, the Grand Slams reversed course and made the decision to award prize money and allow professional players to compete. It has proven to be an immensely successful move that has helped lift the sport to new heights.
The first match of the Open era was played on April 22, 1968, when Australian Owen Davidson defeated John Clifton of Great Britain in the first round of the British Hard Court Championships.
The 1968 US Open was won by Arthur Ashe (pictured above with his father, after winning the 1968 title), who defeated Dutchman Tom Okker in the final.
For more on the start of the Open era, as told by tennis trailblazer Davidson and International Tennis Hall of Fame journalist Steve Flink, check out this month's edition of Courtside, the official podcast of the US Open.