No Matter How You Slice It, a Stealthy Backhand Still Works

Calla Kessler/The New York Times

Roger Federer and Ashleigh Barty strode toward the weekend at the United States Open dogged by a question.

Were they still suffering from the Wimbledon blues?

Federer, the men’s No. 3 seed and an eternal fan favorite, arrived at his third-round match on Friday after a pair of error-laden performances in which he’d looked uncharacteristically weary.

At age 38, after reaching the Wimbledon final in July only to lose an epic marathon to Novak Djokovic, did Federer have a hangover?

And what about Barty, the second-seeded woman? In June, the stylish Australian took the French Open title and vaulted briefly to No. 1 in the rankings for the first time. Then came a…