Over the last few years, Novak Djokovic has shown a penchant for some big-time performances at the Major tournaments, especially the hardcourt ones.
The Serb's game seems to suit hardcourt better than any other surface. He can absorb his opponents' big strokes and redirect them with interest, and his flexibility allows him to maintain his balance even when he's on the move.
But these technical attributes are just a small part of what makes Djokovic dangerous. The Serb has a very competitive mentality and looks to win at any cost.
There are still only a select few entities in the world who can beat the three-time US Open winner. Some of them are non-living things. And yes, even Carlos Alcaraz on his own can't put away Djokovic yet, unless the Serb finds ways to sabotage himself.
Here is a list of the five things that could stop the Serb from triumphing at Flushing Meadows this year:
#5 Humidity
At last week's Cincinnati Open, Novak Djokovic was visibly struggling with the extreme humidity during the first set of his championship bout with Alcaraz. The humidity, along with the summer heat, troubled the Serb greatly as he dropped the opening set 7-5.
However, due to a blip in focus by his younger opponent in the second set, Djokovic was able to wrest control of the match and eventually seal the victory in three tough sets.
Humidity has always been one of the 36-year-old's sworn enemies. At the 2018 edition of the New York Slam, Djokovic went as far as to call for air-conditioning appliances courtside to help deal with the sweltering humidity, which had made him sweat profusely in his early-round matches.
Djokovic looked sapped of all of his life force at one point during his 2018 US Open quarterfinal match against John Millman, leading many to ponder whether he could've retired due to the conditions.
But the 23-time Major winner didn't give in and subsequently had cooler conditions in his semifinal and final matches, which allowed him to win his third title in Flushing Meadows.
#4 Heavy balls & high-bouncing surface
There is a reason why Novak Djokovic has won significantly more Australian Open titles than he has won US Open titles.
The surface in Melbourne doesn't allow the ball to drop too high thanks to the GreenSet Cushion system, which neutralizes the effects of a topspin-laden ball on the surface.
The surface employed at the US Open is starkly different, though. The ball tends to bounce a bit higher than it does in Melbourne due to the different nature of the hardcourt's base material.
This disturbs Djokovic's racket trajectory, which in turn hurts his accuracy against the top players.
Moreover, the Serb has historically struggled to create pace off his own forehand, especially during the US Open finals against the likes of Rafael Nadal and Stan Wawrinka.
It was revealed last year that the US Open employs a heavy type of Wilson ball in the men's competition, thereby necessitating players to take big cuts on the green fuzz in order to penetrate the court.
Djokovic, however, has struggled to create his own pace with passing age, due to a variety of issues. His elbow and shoulder are seemingly not as strong as they used to be, and had their own niggles earlier this year.
In that context, if this year's US Open employs the same set of heavy-duty balls, then the Serb could have a relatively tough time at Flushing Meadows.
#3 Djokovic's lack of preparedness due to easy draw
Yes, that is exactly what it sounds like. Bear with us. Sometimes in his career, Novak Djokovic has had it so easy at an elite tournament that when he got to a marquee match, he wasn't in a good enough rhythm, as he hadn't been challenged to raise his game in his previous matches.
The Serb was seemingly afflicted by this very issue at this year's Wimbledon, where he lost to Alcaraz in the final. His Cincinnati final, meanwhile, almost went off the rails as he took a fair bit of time to get into his groove.
Another slight worry for Djokovic fans would be that all of his top rivals - Alcaraz, Daniil Medvedev, Alexander Zverev, Jannik Sinner - have been grouped in the top half of the men's singles draw.
In the past, some of Djokovic's greatest Major title victories have warranted that he beat back-to-back top players. Conversely, when his early round matches have been handed to him easily - like the US Open 2016, where three of his opponents retired due to injury - he has failed to sharpen his game and mentality for the final.
This, however, is a very minuscule concern, as tennis matches are usually not decided by such relatively arbitrary reasoning but by actual skills.
#2 Opponents who can hit deep and flat
Novak Djokovic is a tenacious baseliner with possibly the best defensive skills in the history of tennis. He likes to change the direction of his shots with his wristy forehand while standing near the baseline. The 36-year-old also hits very deep groundstrokes, not allowing his opponents enough time to attack him.
Having said that, Djokovic has occasionally struggled with his cross-court forehand over the last few years. He can't hit huge groundstrokes from the back of the court, and sometimes his cross-court shot fails to have enough depth on it.
To take advantage of this shortcoming, his opponents need not necessarily hit huge groundstrokes but deep, penetrating ones instead, so that the impetus is on the 36-year-old to create his own pace.
In the past, Medvedev has been able to trouble the three-time US Open champion with his metronomic, flat style of play. But the Russian is not in Djokovic's half this time.
There are, in fact, very few players in the Serb's half who play the style of tennis that is ideal for beating him. All of his projected top-seeded opponents, like Stefanos Tsitsipas, Holger Rune, and Casper Ruud, like to play with loads of spin on their shots.
For what it's worth, Djokovic can face the familiar Jiri Vesely in the fourth round, provided the unseeded Czech navigates through his section of the draw. Vesely, who leads the 23-time Major winner by a margin of 2-0 in their h2h, plays a very aggressive, flat ball, which hurts the Serb's rhythm.
Another player whose style of play bothers the Serb is Sebastian Korda, who almost beat him in Adelaide earlier this year. The American swipes through the ball with insane racket head speed and depth, but he will have to beat Ruud and Rune before he can face Djokovic.
#1 Carlos Alcaraz and the American crowd
During this year's Wimbledon final against Carlos Alcaraz, Novak Djokovic was troubled a lot by his nerves, and there were several inopportune moments when he failed to connect with the ball properly.
The Serb's carelessness ended up costing him the second set, following which the English crowd began cheering raucously for his opponent.
Their wild reactions seemed to mildly offend the Serb. In the fifth set, when Alcaraz won a scintillating rally to take the decisive break lead, the Serb was again flustered by the crowd's reaction and the situation he found himself in.
These circumstances prompted him to destroy his racket by hitting it at the net post. He would go on to lose the match in five tumultuous sets.
The American crowd is known to be even more hostile than the English crowd. And Djokovic himself had a run-in with them during the 2015 US Open final against Federer.
A large majority of the crowd was cheering against the Serb that day. But he wasn't to be bogged down, as he zoned out from the noise and played some of the best tennis he had ever played.
Djokovic is eight years removed from that day in Flushing Meadows though, and his hunger for winning might be a bit less than it was back then. Also, the New York crowd essentially adopted Alcaraz last year, thanks to his entertaining style of play.
So if Alcaraz can win his first six matches, he has a genuine chance of upsetting (pun intended) the 23-time Major winner in the championship match.
How did Novak Djokovic meet Jelena Ristic? All about the most admired couples in tennis