The signs were there before the United States Open began, even if many people refused to recognize them. Roger Federer had injured his 36-year-old back earlier, during a tournament in Montreal two weeks ago, then had withdrawn from the next tournament in Cincinnati to rest it.
There were more signs in his first-round match against Frances Tiafoe, when Federer’s famous one-handed backhand looked uncharacteristically weak and ineffective. He required five tense sets to beat an American teenager playing in his first match at Arthur Ashe Stadium.
Federer, the third seed, insisted that his back was not an issue, although he is also not one to make excuses for rare losses and poor play.