Rafael Nadal celebrates during a U.S. Open men's semifinal match...

Rafael Nadal celebrates during a U.S. Open men's semifinal match against Juan Martin del Potro on Thursday Sept. 8, 2017. Credit: Newsday / J. Conrad Williams Jr.

For one set, anyway, the U.S. Open had the next best thing to a long-anticipated Rafael Nadal-Roger Federer semifinal. For one set, former Open champ Juan Martin del Potro filled in admirably for Federer, whom del Potro ousted in Wednesday’s quarterfinal.

But Nadal, second only to Federer in career major-tournament titles with 15, quickly forced a tipping point and powered to a 4-6, 6-0, 6-3, 6-2 victory Friday night. That puts Nadal, at 31, through to his 23rd major-tournament final, and his fourth U.S. championship match. He won two of the first three, in 2010 and 2013.

“After a couple of years of problems and injuries,” Nadal said, “this year has been very emotional.”

Nadal’s transformation Friday night from an early free fall to floating peacefully to safety by opening his parachute of tennis expertise was sudden. And complete. He won nine straight games spanning the second and third sets and didn’t allow del Potro a look at a single break point after two [one converted] in the first set.

“I was not playing bad the first set,” Nadal said, “but I was losing. Too much against his backhand, so I had to change something.”

For the first 50 minutes, del Potro’s walloping groundstrokes and aggressiveness offered a challenge for Nadal. Both Spain’s Nadal and Argentina’s del Potro have been enormously popular with Flushing Meadows crowds for years, and the roar-ripping joust in the first set had the Arthur Ashe Stadium fans alternately in riotous cheers for Nadal’s particular art form of offensive defense, and ringing Ole! Ole! chants for the powerful del Potro.

They were a couple of working-man heroes, their loud grunts echoing with their effort. Between points, the 6-6 del Potro was stalking the baseline, while the muscular, caffeinated Nadal was fidgeting, bouncing on his toes.

When they traded rundowns of each other’s short ball, each producing a delicate, angled tap past the other after a long ninth-game rally, the building was up for grabs. But the lovely war didn’t last. Nadal pounced on a break point in the second game of the second set and kept del Potro in a painful vice.

Though Nadal’s status as world No. 1 and top seed theoretically put him out of reach of the 24th-seeded del Potro, the Argentine is one of only two players — Novak Djokovic is the other — to have beaten Nadal and Federer in the same Grand Slam event. That’s how del Potro won the 2009 Open (and how Djokovic won the 2011 Open).

Del Potro, among players never ranked No. 1, has beaten a No. 1 more often — eight times — than anyone since that statistic first appeared 33 years ago.

But del Potro’s series of four wrist surgeries has put a significant ouch in his career. And, while he bounced back from a stomach illness that couldn’t keep him from a five-set victory over No. 6 Dominic Thiem in the fourth round and then took down Federer, del Potro’s stamina began to crater much too early last night.

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