NEW YORK >> Japan’s Kei Nishikori became the first man from Asia to reach a Grand Slam final, stunning top-ranked Novak Djokovic 6-4, 1-6, 7-6 (4), 6-3 in stifling heat Saturday at the U.S. Open.

“It’s just amazing, an amazing feeling beating the No. 1 player,” Nishikori said during an on-court interview.

He had played five-set marathons in his last two matches totaling more than 8 1/2 hours, yet he looked far fresher than a player known as one of the fittest on tour.

“He just played better in these conditions than I did,” Djokovic said.

Under coach Michael Chang, the 1989 French Open champ, the 24-year-old Nishikori has sharpened his mental game to pull out victories like these.

“We’ve been working super well,” Nishikori said, referring to Chang and co-coach Dante Bottini. “That’s why I’m here.”

The 10th-seeded Nishikori will face Roger Federer or Marin Cilic in Monday’s title match, though rain was delaying the start of the second semifinal.

Earlier, the midday sun beat down on Arthur Ashe Stadium and a thermometer on court showed the temperature nearing 100 degrees (37 Celsius), not counting the humidity of close to 70 percent. Nishikori closed this one out in 2 hours, 52 minutes.

Djokovic, who had reached the last four U.S. Open finals, outlasted two-time major champ Andy Murray in four long, tough sets in the quarters. But he never looked comfortable Saturday and spent much of the match scrambling around the court as Nishikori dictated points.

“Just wasn’t myself,” Djokovic said.

In the third-set tiebreaker, Djokovic had four unforced errors and a double-fault. Nishikori then broke to open the final set, and Djokovic wasted three break points in the next game.

Nishikori converted 5 of 7 break points, while Djokovic was just 4 for 13.

“Other than that second set, my game today was not even close to what I wanted it to be,” Djokovic said. “A lot of unforced errors, a lot of short balls.”

Chang, the New Jersey-born son of Taiwanese immigrants, knows a thing or two about groundbreaking victories. At age 17, he became the youngest man to win a Grand Slam title when he upset Ivan Lendl and Stefan Edberg (now Federer’s coach) at Roland Garros.

A severely infected right big toe forced Nishikori to miss tuneup events before the U.S. Open, and he feared that his lack of conditioning would make for a short stay at Flushing Meadows. Instead, he keeps sticking around — on the court and in the tournament.

“I guess I love to play long matches,” he said with a grin.