Rafael Nadal enters the court slowly, somberly, every ounce of him emanating stolid focus. He is locked in. One gets the feeling, watching him strut, that if he were to walk into a wall at this moment, it would be the wall that crumbles.

It is a look we see from him often, viewing him on court in a tense match.

But this is not a match. It’s practice.

It’s happening on the grounds of the United States Open, where Nadal has reached the quarterfinals in his drive for his 19th major title. It’s happening at noon on Tuesday, 14 hours after his late-night, four-set win against Marin Cilic — a contest in which he’d played with his hallmark hammering style from the first point to the last.

On Wednesday, Nadal faces the Argentine Diego Schwartzman, whose punishing groundstrokes and court savvy seem prime to produce a marathon fight.