The time players take between points has been a constant topic of debate in recent years.
Some players like Rafael Nadal and Novak Djokovic have been accused of taking too long to play between points.
While others like Roger Federer and Nick Kyrgios have always played quickly and avoided any controversy.
But for the first time at a Grand Slam, the US Open has brought in a shot clock to speed up play and avoid time wasting.
Players will also have just one minute from the time they walk onto the court to meet at the net for the coin toss with the umpire then a five-minute countdown to warm-up and start play on time.
What is the shot clock?
The shot clock is a 25-second countdown from the end of a point to serve for the next one.
Why is it being introduced?
USTA spokesman Chris Widmaier said: “Pace of play is a major issue in sports today.
“We recognize that and we want to be ahead of it.”
Can the players see the clock?
The shot clock is visible to players on the side of the court and fans in the stands.
What are the punishments for going over 25 seconds?
The first time a player goes over the 25 seconds, they will be given a code violation by the umpire.
The second time it happens, the player loses a first serve.
What does Rafael Nadal think of the shot clock?
Nadal has been caught out by the shot clock during the tournament but the Spaniard insists he is comfortable with the new policy.
He said: “I played in Toronto with the clock. So when I said that before the tournament, you can check what I said because my answer will be the same. I played in Toronto with the clock.
“The only thing that in my opinion is good is that the umpires are doing a good job. If they are doing the things the right way, that they wait to put the clock on when the points are so long, is not a problem.
“Clock, in my opinion, is just a part of the show. If they do it too strict, I believe especially under some tough conditions, the show is worst because you can’t play a couple points in a row, great rallies, with no time to recover.
“But in my opinion, they are doing a very good job.”