Rafael Nadal, Novak Djokovic  have winning history against opponents  in U.S. Open semifinals

    “To be honest with you,” John Millman said, “I think in a day or two time I will be yesterday’s news, you know. There’s going to be a champion of this tournament, and they should be the story.”

   He is right, of course. For a couple of nights on the big Arthur Ashe Stadium stage Millman, a 29-year-old journeyman who was stuck in the tennis minor league for years, provided something to talk about at the U.S. Open. Now, quickly, the page is turned to Friday’s men’s semifinals and familiar faces: Three-time Open champion Rafael Nadal against Juan Martin del Potro, the tournament’s 2009 winner; and two-time Open champ Novak Djokovic against 2014 runner-up Kei Nishikori.

   So farewell to Millman, whose ambush of five-time Open titlist Roger Federer in the fourth round and legitimizing work in a straight-sets quarterfinal loss to Djokovic made him a sudden star in his native Australia.

   Now he’s gone. Furthermore, what also could suddenly disappear are the smothering conditions — high heat and humidity — that have been a major narrative in this year’s tournament, called by Djokovic “the toughest U.S. Open in the years I have played. I personally have never sweat as much as I have here. Incredible. I mean, I have to take at least 10 shirts for every match.”

   It was the sweltering stillness in Ashe Stadium that Federer cited as his major problem during his upset loss to Millman (and that caused fellow players to marvel that they never had seen the perpetually cool Federer sweat before). With more reasonable temperatures, the talk surely will focus entirely on the player matchups.

   Defending champ and top-ranked Nadal has a career 11-5 edge over del Potro and leads 5-1 in major tournament duels. This will be the third consecutive Grand Slam event in which they have met and fourth time in the last five Slams, with Nadal winning semifinals in last year’s U.S. Open and this year’s French Open, as well as a five-set quarterfinal two months ago at Wimbledon.

   But that doesn’t blunt the third-seeded del Potro’s eagerness to try again. “Of course, I like to play always with the No. 1 in the world,” he said. “It doesn’t matter the tournament or the conditions or the weather. I just have the chance to play the greatest in this sport, and that’s amazing to me.”

   Nadal suspected Friday’s skirmish will be “a very tough one. Juan Martin in Wimbledon was a great player. He’s great on grass. Well, he’s a great player anywhere, but the challenge of playing him on hard court of course is ever higher for me personally than playing him on clay, like happened in Roland Garros” — a straight-sets Nadal decision.

   Djokovic, seeded sixth at the Open, brings a dominant head-to-head record of 14-2 — with 13 consecutive victories — against No. 21 Nishikori. The last time he lost to Nishikori, in fact, was the 2014 U.S. semifinals, before Nishikori lost the final to Marin Cilic.

   “Well, yeah, I don’t have a great record against Novak,” Nishikori said. “I see a chance, but I haven’t been able to make the last step. But always excited to play Novak, because he’s a great challenge for me.”

   Djokovic, for his part, wasn’t about to prepare any victory acceptance speeches before the results are in. “I mean, I can’t really say he’s a great matchup for me,” Djokovic said. “I have a very good head-to-head score against him. But, if not the quickest, he’s one of the quickest players on the tour. He has phenomenal footwork. I know I have to be at my best.”

   John Millman reminded the top players of that necessity.