That does not bode particularly well for the oft-injured Anderson. He possesses a powerful serve that could theoretically trouble Nadal in their fifth head-to-head encounter on Sunday. But Nadal won their four previous meetings and has the experience of winning 15 major titles, second only to Federer’s 19. He also earned his 15th consecutive Grand Slam semifinal victory, a streak that began after del Potro beat at the U.S. Open in 2009.

Nadal has played much of the year like a rejuvenated champion, reaching the Australian Open final, where he lost to Federer, and soaring during the clay season to notch his record 10th French Open.

He has not been perfect during his run in New York, but he is getting stronger, combining his relentless defense with an increasingly sharp serve and the shrewd tactics of a veteran clay-court specialist.

“He played so smart from the second set till the end of the match,” del Potro said.

After a first set in which Nadal seemed reluctant to hit the ball to del Potro’s high-powered forehand, Nadal summoned his strategic acumen to change the course of the match.

He had been peppering del Potro’s weaker backhand cross court with his lefty forehand, but del Potro was equal to the challenge, at least in the first set. He camped out on the ad side of the court and waited for the right moment to hit penetrating backhands down the line.

Nadal was frustrated, but between sets, he switched to Plan B. No matter how frightening del Potro’s forehand might be, Nadal would have to hit to that side, if only to erase his predictability and force del Potro to move. No longer able to stand in the corner and set his feet, del Potro struggled. He had also just come off two difficult matches in the previous rounds and an illness, and Nadal made him pay for all if it.