Now that the U.S. Open is in full swing, keep your eyes peeled for Andre Agassi, Andy Roddick . . . and Anthony Falco Jr., better known as A.J.

He’s is a lot harder to spot. The 12-year-old Brooklyn kid is one of the tennis tournament’s ball boys, and this is his third Open.

A.J. started playing nine years ago, when he was 3 and saw his older cousins hitting the ball back and forth. He asked their tennis coach to let him join in – and A.J.’s hardly stopped swinging a racket since.

Most ball boys and girls are 14 or older, but A.J.’s coach asked him to try out anyway. He made the cut, but he works for free: The older kids get paid $7.75 an hour.

Truth is, A.J. says, he’d pay just to be there.

“One thing I like about the game is you don’t know what could happen,” he tells The Post. “A great player can have a bad day, and a good player could have a great day.”

A.J. also volunteers with the EPVA (the Eastern Paralyzed Veterans Association), helping people in wheelchairs play tennis.

Here’s what else he told us:

Q: How many ball kids work a game?

A: We have six on each court for every game: two on each side, two at the net, two at the back.

Q: How many balls do you retrieve during a typical match?

A: A lot!

Q: Do you get to take any home?

A: No.

Q: Who’s your favorite player?

A: Andre Agassi. He has great returns – when someone serves to him, he puts it away.

Q: Get any autographs?

A: Nope. You’re not allowed to.

Q: What do you want to be when you grow up?

A: Maybe a tennis player. Or a lawyer.