On second serves, attacking down the middle can also be more effective then aiming for corners, Gilbert said.

Paul Annacone, a Tennis Channel analyst, said going for a corner or a short angle either led to misses or, if the shot was too cautious, gave the server an angle and an open court.

“If you don’t hit a perfect return going for the angle, then it becomes a track meet in lateral tennis, and the server usually has the advantage,” he said.

The deep middle return is so effective, Navratilova said, because the server is still off balance — hit it deep enough and they have to backpedal — and it is difficult for them to hit their first shot with pace or depth. “It’s gold,” she said.

Annacone said the middle return reduced reaction time for the server and also gave the player less space to hit a sharply angled shot of their own.

The shot is least useful on red clay where servers get extra time to recover, Navratilova said.

It’s most dangerous on the grass at Wimbledon, where the ball skids and the grass gets patchy, producing unusual bounces and poor footing. (Federer used this return to great effect during July’s Wimbledon quarterfinals against Kei Nishikori. ) Annacone said that while the hard courts at the U.S. Open lacked those benefits, they were fast enough to make the deep middle return a genuine weapon.

On the men’s side, the shot is particularly effective against the players who are 6-foot-5 or taller.