Rafael Nadal, left, will take on Juan Martin del Potro,...

Rafael Nadal, left, will take on Juan Martin del Potro, right, in the U.S. Open men's semifinal Friday. Credit: DANEIL MURPHY

Assuming the roles of adversaries in one of Friday’s U.S. Open men’s semifinals will be a pair of understudies, Pablo Carreno Busta and Kevin Anderson.

Of course, there is no lack of star power in the other semi, even with Juan Martin del Potro’s quarterfinal elimination of The Man Who Needs No Introduction, Roger Federer. Del Potro, the 2009 Open champ and longtime spectator favorite at Flushing Meadows, will take on the wildly popular Rafael Nadal.

But with all due respect to Carreno Busta and Anderson, they could use some preliminary remarks on their backgrounds and credentials. It is difficult to cite such a duel of outliers in the Open’s penultimate round since France’s Cedric Pioline defeated Australia’s Wally Masur in 1993.

Dutchman Sjeng Schalken made it to the 2002 semis, but he faced Pete Sampras. And promptly was dismissed.

So here is No. 12 seed Carreno Busta, a 26-year-old Spaniard who turned pro in 2011 and, in 15 previous Grand Slam appearances, got past the third round only once, at this year’s French Open.

With the Carreno Busta-Anderson half of the draw having its top four seeds — No. 4 Alexander Zverev, No. 5 Marin Cilic, No. 8 Jo-Wilfried Tsonga and No. 10 John Isner — out by the third round, Carreno Busta’s first four matches were against qualifiers, He has not lost a set.

“I know I didn’t win matches against top players,” he said. “But when you have this draw, you have to do your best to take advantage, so I think this is a very good tournament for me.”

Anderson, too, has made the best of his chances. A 31-year-old South African who was an All-American at Illinois and resides in Florida, the 6-8 Anderson, seeded 28th, is in his 34th major tournament — and beyond the fourth round for the second time. (He lost to Stan Wawrinka in the U.S. quarterfinals in 2015.)

Like Carreno Busta, Anderson didn’t face a seeded player until the quarters, when he eliminated Sam Querrey.

“This is new ground for both of us,” Anderson said of himself and Carreno Busta, against whom he has won two previous meetings. “Yeah, we are all so accustomed to, for a decade, the same guys being there, and they’ve had such unbelievable consistency.”

That consistency is what generated expectations that it would be Federer — five times the Open champion and a record 19 times a major-tournament titlist — in Friday’s semi against Nadal, winner of 15 Slam events. Del Potro, hounded by a series of wrist surgeries, still is looking for a second Grand Slam title.

But after his four-set loss to del Potro, Federer concluded that the latter “deserved it more” and “will have a better chance to beat Rafa, to be honest. The way I’m playing right now is not good enough.

“Of course you’re disappointed when you lose. It’s terrible to think of what lies ahead, packing bags, going home,” he said. “But you run into guys who are better than you on the night. Juan Martin fought like a lion.”

Federer declared that the Nadal-del Potro semi “is going to be exciting.” And one of those other guys is about to become a U.S. Open finalist.

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