“Novak’s back at an amazing level, hitting the ball very deep and hitting his spots so well with the serve,” Dante Bottini, one of Nishikori’s coaches, said. “Kei didn’t play his best game today, but he came up with some very good shots, and Novak came up with the same or better. But I still think the final is going to be very tough.”

It will be the first Grand Slam final between Djokovic and del Potro, but hardly their first high-stakes duel. Djokovic leads the head-to-head by 14-4 and has won six of their last seven encounters, including their best match, a classic five-setter in the semifinals of Wimbledon in 2013.

But del Potro’s lone victory of late — in the opening round of the Olympic Games in Rio de Janeiro in 2016 — was one of the blows that sent Djokovic reeling in earnest.

“The heartbreaking loss in the Olympic Games, that hurt me a lot, and that’s probably where I spent everything that was left in the tank,” he told ESPN recently.

At that stage, he still held all four of the Grand Slam singles titles, including the U.S. Open, which he had won in 2015 by defeating Roger Federer in front of a hostile crowd with the help of some mind games.

“They would scream, ‘Roger!’ and I would imagine they were screaming, ‘Novak!’ ” he explained then.

He has yet to be fully embraced in New York, and though he will be the rightful favorite against del Potro on Sunday, it is hard to imagine he will be the crowd favorite.

Del Potro’s comeback story is on another level. It has been nine years since he played in his first Grand Slam final at the U.S. Open, rallying to defeat Federer in five sets to win in 2009. Since then, there have been four wrist surgeries, including three on his left wrist, which had him understandably contemplating retirement in 2015.