He just keeps going, keeps winning and, in particular, keeps beating Taylor Fritz. No. 7 seed Novak Djokovic is into the US Open semifinals after defeating the fourth-seeded Fritz 6-3, 7-5, 3-6, 6-4 on Tuesday night. He is now 11-0 against Fritz.

Djokovic put the pressure on Fritz from his very first service game, in which Fritz faced three break points and was only able to save the first two. In the very next game, Fritz got a break point opportunity but returned Djokovic's serve into the net.

Fritz would get another prime opportunity -- several of them, actually -- to get back on serve. With Djokovic leading the set 5-3, Fritz earned two break points lead but failed to convert either, including an incredible 25-shot rally that Djokovic ultimately won.

Fritz then had three more break opportunities but failed to convert any of them with Djokovic showing his phenomenal defense, return game and poise -- all pillars of his historic career.

Fritz, however, seemed to find his footing -- and his confidence -- in that game, and it showed to start the second set. He produced a pair of easy holds and got another break chance up 2-1. Again, Djokovic produced a masterpiece to get another hold, a magnificent crosscourt winner while stretching to his right.

With Fritz's frustration mounting having gone 0 for 9 on break point chances to that point, Djokovic took advantage, breaking a careless Fritz to take a 4-3 lead.

Shortly thereafter, Fritz converted a break point. Djokovic, serving for the set, fell down 0-40 and then dumped a drop shot into the net. At five games apiece in the second, Arthur Ashe Stadium erupted.

As soon as he seemed to have momentum, though, Fritz's serve abandoned him, and he double-faulted away his service game. This time, Djokovic held serve in straightforward fashion, putting away the second set, 7-5. Fritz left the court between the second and the third set, hoping to collect himself.

It helped. So, too, did the crowd. On serve early in the third set, Djokovic started hearing some jeers and approached the chair umpire for help. There wasn't much he could do, though, and Fritz converted a break opportunity, running down a Djokovic drop shot and putting an emphatic forehand winner away.

This time he wouldn't repeat his mistake from the second set. Rather, he stepped up his serving after the hard-earned break to take the set 6-3. He produced seven aces and won 90% of his first-serve points in the set.

The fourth set seemed bound for a tiebreak with both men serving well, but down 5-4 on serve, Fritz went down 15-40, his serves once again going awry at the worst time. He managed to save two match points with tremendous baseline play but then double-faulted away the match, a devastating ending against the man he remains unable beat.

During his post-match interview with ESPN, Djokovic admitted he thought Fritz was the better player in the middle two sets. The difference, it turned out, was a few crucial points. Djokovic converted four of nine break chances; Fritz was two for 13. Fritz also had 42 unforced errors, compared to Djokovic's 40. 

It's yet another loss that left Fritz shaking his head in disbelief and many viewers doing the same regarding his opponent: How does Djokovic, at 38 years old, keep doing it? He'll have to reach an even higher level next. He faces No. 2 seed Carlos Alcaraz in the semifinals. Alcaraz is yet to drop a set this tournament.