Frances Tiafoe talked a big game and delivered a bigger one. 

Greatness was predicted for Tiafoe when he broke onto the scene eight years ago with his speed and power. He finally showed that skill set that had everyone agog when he was 16. And then he broke down in tears after match point when he achieved Monday’s milestone. 

Before the Round of 16 matchup, Tiafoe expressed confidence he could knock out Spanish legend Rafael Nadal and post the largest win of his as yet unfulfilled career. 

The 24-year-old American blasted through at Arthur Ashe Stadium on Labor Day before a manic, pro-Tiafoe crowd to upset Nadal with a blistering serve and forehand to make his first Open quarterfinals. 

Tiafoe, the 22nd seed, stunned No. 2 Nadal 6-4, 4-6, 6-4, 6-3. It was the first time the 36-year-old Nadal lost to an American at a major in 17 years when he was beaten by James Blake. 

Tiafoe’s first reaction after the handshake was crying into a towel. 

“I felt the world had stopped,’’ Tiafoe said. 

“I’m beyond happy — almost in tears,’’ he said on court. “He’s definitely one of the greatest of all time. I played unbelievable tennis today. I don’t know what happened.’’ 

What happened was he made good on his bold prediction. Before the match, Tiafoe had said, “I’m not going to have that first-time-playing-him, excited-to-play [feeling]. Now I believe I can beat him.’’ 

Afterward, Tiafoe wasn’t short of confidence. “I’m here to win the U.S. Open,’’ he said on ESPN. “I’m here to go all the way.’’ 

Tiafoe was still trying to get in Nadal’s head — staring him down on a few occasions after a big point. 

A Washington-area native and Wizards fan, Tiafoe saluted a friend, superstar Bradley Beal, attending his first tennis match. 

But Tiafoe was floored LeBron James tweeted a shout-out calling him “young king.’’ NBA superagent, Rich Paul, sent him a congratulatory text. 

“Man, I was losing it in the locker room,’’ Tiafoe said. “Bro, I was going crazy. That’s my guy. So to see him post that, I was like, ‘Do I retweet it as soon as he sent it?’ I was like, ‘You know what, I’m going to be cool and act like I didn’t see it and then retweet it three hours later.’ ’’ 

Meanwhile, Nadal wasn’t sharp all tournament as he underwent abdominal surgery after withdrawing from Wimbledon in the semifinals. Tiafoe made him look worse, serving 18 aces, including a few clocked above 134 miles per hour. 

Still, Nadal felt he wasn’t Nadal. And the lefty bull occasionally looked his age — 36 — not just because of thinning hair. 

“I played a bad match and he played a good match,’’ said Nadal, who hit nine double faults. “I was not quick enough in my movements. Tiafoe is playing more solid than before, serving well, taking the ball very early. He’s quick. But I don’t think I pushed him enough to create the doubts that I need to create.’’ 

Novak Djokovic, who missed the Open because he wouldn’t get vaccinated, should send a thank you note to Tiafoe. Nadal stays at 22 Grand Slam titles and fails to widen his lead over the Serbian, who has 21. 

“Of course, this was not the ideal preparation for me,’’ Nadal said. 

Tiafoe won the first set, breaking Nadal at 3-3 after the Spaniard hit a forehand long. Tiafoe closed the first set with an ace. 

Nadal then took a “bathroom break’’ of 8 minutes, 30 seconds that angered Tiafoe, who kept checking with the umpire about the legality. Nadal said it wasn’t a medical timeout, he was attaching wraps to himself because of the humid conditions. 

Bathroom breaks are usually three minutes long and the USTA said it was looking into the matter. 

Nadal was a new player and raced past Tiafoe in the second set, but he ran out of steam. The American didn’t get frustrated by Nadal’s shenanigans. He got right back into firing lethal forehands past Nadal. 

At 4-4 in the third set, Tiafoe flew up 40-15 and won the game with a crushing forehand winner. He closed the set out with an ace and ran to his chair — a sign he had plenty left in the tank. 

Again, Nadal left the court, after the third set and Tiafoe just followed him out. In the fourth, Nadal broke early, Tiafoe broke back, and then fought off two break points to even it at 3-3. Tiafoe said pulling that game out was key because “my legs were cement.’’ 

Then he posted his second break of the fourth set and cruised home to his historic victory with a date against eighth seed, Russian Andrey Rublev on Wednesday. He’ll have the crowd. 

“I probably couldn’t beat Nadal anyplace else,’’ Tiafoe said.