Coco Gauff, the most popular American tennis player, hadn’t been able to book a practice court. So, she and her newly hired coach, biomechanics expert Gavin MacMillan, braved the mist for close to an hour as they worked on trying to fix her serve.

Gauff said, "I'm obsessed with the process of getting better. ...I feel like I have a clear future where I see myself and I feel like I'm really close."

Coco Gauff was as aware as anyone, of course, that her tour-worst double-fault total is a significant problem, so she fired one of her coaches on the eve of the U.S. Open and brought aboard the serve doctor who helped No.