The pitter-patter of little feet could be heard all over the court as the ball kids went to work.
"Hustle, hustle. Everything's about moving fast," says Coach Jim Brownell to one of the kids.
Brownell teaches the kids to either move like lightning or freeze as though they were statues to become almost invisible.
There are six to eight ball kids working each match. It is Brownell's job to turn them into a synchronized ball-returning machine.
"You have the best seat in the house and as far as I'm concerned, you have the most important job in the whole tournament. Aside from the players earning a paycheck and playing for a ranking, you are the most important person on the court," says Brownell.
These kids are all tennis-loving teenagers.
"Well at the net you always have to pay attention to everything, especially tie-breaks. Tie-breaks are definitely the hardest because the points just go from side to side very, very quickly," says aspiring ball kid Monica Chang from Los Altos.
Being up-close to pro tennis players is one of the perks of the job.
"It's sometimes surreal and ... it just feels like, wow, they're right in front of you," says aspiring ball kid Paulina Bajet from Newark.
"You might be getting a serve towards you at a 100 miles an hour. I want you focused on where the balls are," says Brownell to the kids.
Mark Nielson played a match to help the kids tune up for the Bank Of The West Classic and having a little help out there was a treat for him.
"Well playing my game, especially these days as I'm getting a little bit older, all of the extra help. Less movement is always a good thing," says Nielsen.