The US Open has not been a happy hunting ground for unseeded players in recent years. Only four unseeded players have managed to progress to the quarterfinals in the last 11 editions -- Grigor Dimitrov (2019), John Millman (2018), Andrey Rublev (2017), and Juan Martin del Potro (wildcard in 2016).
Out of those four, Dimitrov is the only player who went on to reach the semifinals. But this year, unseeded players will have a great opportunity to make their presence felt as a host of top names will be missing.
Five-time champion Roger Federer, four-time champion Rafael Nadal, 2016 winner Stan Wawrinka, defending champion Dominic Thiem and former Wimbledon finalist Milos Raonic have all pulled out of the year's final Grand Slam.
Meanwhile, 2014 runner-up Kei Nishikori's prospects are bleak. Nishikori played well at the Citi Open earlier this month and ideally would have been a dark horse at the US Open.
However, he handed a walkover to Hubert Hurkacz at the recently concluded Cincinnati Masters which casts doubt over his fitness ahead of the hardcourt Major.
On that note, here's a look at five unseeded male players who could wreak havoc in the main draw at the 2021 US Open.
#5 US Open debutant Carlos Alcaraz
World No. 54 Carlos Alcaraz is predominantly a claycourter. He recently won his maiden ATP title on the red dirt at the Umag Open last month.
So what is he doing on this list ahead of the likes of Mackenzie McDonald, Brandon Nakashima, Marton Fucsovics, and Taylor Fritz who are all more experienced on hardcourt and have posted better results on the surface? The reason is the huge improvements he has made to his game over the past year.
The 18-year-old came through three qualifying rounds at the Australian Open earlier this year and made it to the second round of the main draw before losing to Mikael Ymer.
Alcaraz went one step further at the French Open, reaching the third round, where he lost to Jan-Lennard Struff. The Spaniard then made it to the second round at Wimbledon on his debut.
Alcaraz is currently into the quarterfinals of the Winston-Salem Open at the time of writing. He defeated Alexei Popyrin and Marton Fucsovics en route to the last eight, an impressive feat considering Popyrin and Fucsovics' prowess on hardcourt.
Alcaraz will be playing in his first-ever US Open and will be hoping to pull off an upset or two.
#4 Lloyd Harris
Lloyd Harris has never gone beyond the second round of the US Open in three previous attempts. But the South African could do some damage this year if his recent performances are anything to go by.
Harris beat Rafael Nadal at the Citi Open before running Reilly Opelka extremely close at the Toronto Masters. He even went toe-to-toe with Alexander Zverev in the first set of their second-round match at the Western & Southern Open in Cincinnati.
Standing at 6'4", Harris has a potent serve and huge groundstrokes that could work well on the courts at Flushing Meadows.
Moreover, Harris will be buoyed by the fact that he has beaten three Grand Slam champions this year, in the shape of Stan Wawrinka, Dominic Thiem, and Rafael Nadal.
#3 Frances Tiafoe
Frances Tiafoe is no stranger to deep runs at Grand Slams; he made the quarterfinals of the 2019 Australian Open and also the fourth round of the US Open last year.
The American also gave Novak Djokovic a tough fight at the Australian Open earlier this year.
Playing in front of his home crowd will work in Tiafoe's favor. That said, his form during the North American hardcourt swing has been far from inspiring. Tiafoe has lost four of the 10 matches he has played so far, but is into the quarterfinals of the Winston-Salem Open at the time of writing.
#2 Sebastian Korda
Home-favorite Sebastian Korda is one player all the seeds would be keen to avoid in the early rounds. Korda packs a punch with his serve and forehand, and could do some serious damage considering the courts are reportedly faster this year.
Korda will be making his second main-draw appearance at the US Open. The 21-year-old suffered an opening-round exit to Denis Shapovalov at his home Slam last year.
Korda has not been in great form heading into the US Open though; his win-loss record in the North American hardcourt swing stands at 2-2. But like Tiafoe, he could benefit from the backing of a vocal crowd at his home Slam - an advantage none of the Americans could enjoy last year owing to COVID-19 regulations.
#1 Who else but Nick Kyrgios?
As long as Nick Kyrgios is unseeded and healthy, he will always make it onto such lists. Kyrgios is too talented a player to be counted out, no matter how poor his form may be.
Kyrgios has lost three of his four matches leading up to the US Open, with his only win coming against Kevin Anderson in Atlanta. The Aussie also pulled out of the Winston-Salem Open shortly before his first-round match against Andy Murray.
However, it was a precautionary move from Kyrgios as he wanted to protect his body ahead of the US Open.
The Aussie has never made it past the third round at Flushing Meadows in seven previous attempts, but he could be motivated to do well this year.
The mercurial Aussie is a fan-favorite and will undoubtedly receive plenty of support from the crowd provided he does not face an American.
Kyrgios is equipped with a monstrous serve and booming groundstrokes, and could be more than a handful for most players at this year's US Open.
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Honorable mentions: Marton Fucsovics, Taylor Fritz, Mackenzie McDonald, Nikoloz Basilashvili, John Millman, Brandon Nakashima, Emil Ruusuvuori, and Jenson Brooksby.