The US Open can often throw up surprise winners - and this year's Grand Slam finale could be no exception.
With the Olympics taking place just three weeks ago, players are arriving in New York with fewer minutes on a hard court than before, and with more miles in their legs.
"I don't think anyone is coming [to the US Open] in top gear," Christopher Clarey, former New York Times tennis writer, told BBC 5 Live.
"For somebody who is maybe more of a second-tier favourite, this is their year and their opportunity."
Will Djokovic defend his title?
Novak Djokovic is the defending champion, but it remains to be seen if the emotional impact of winning a long-awaited Olympic gold on the Paris clay will affect his chances.
Djokovic made the Olympics his priority this year, but would love to keep his record of winning at least one Slam title every year for the past seven years going.
Victory in New York would secure his 25th major - the most of any singles player, male or female - and make Djokovic the oldest man in the Open era to win a Slam.
"The men's draw is as wide open as it has been for as long as any of us can remember," British player Naomi Broady said on BBC 5 Live.
"This year, especially with the addition of the Olympics and the players being that bit more fatigued, it is going to be incredibly interesting."
Djokovic will face tough competition from world number one Jannik Sinner, who beat him in the Australian Open semi-finals in January, and French Open and Wimbledon champion Carlos Alcaraz.
Sinner is the form player, having won the Cincinatti Open in the build-up to New York.
It was announced earlier this week that the Italian had been cleared of any wrongdoing after twice testing positive for a banned substance in March.
Alcaraz also beat Djokovic in the Wimbledon final, but the Serb got his revenge with a stunning win in the gold-medal match in Paris.
Outside of the top three, last year's runner-up Daniil Medvedev will be eyeing an elusive second Slam, while French Open finalist Alexander Zverev is also a contender.