The dangerous floaters
# 1: Stan Wawrinka (2016 US Open winner)
Stan Wawrinka is one of five Grand Slam champions and former winners at Flushing Meadows this time. The 'other' Swiss beat Djokovic in the 2016 final to win his only title at the US Open.
Seeded 23rd this year, he could have a rematch with the top-seeded Serb in the fourth round, to reach a sixth quarterfinal at the last Grand Slam of the year.
Wawrinka's recent form has been patchy. He has only reached the second week at a Grand Slam once (2019 French Open QF) since finishing runner-up at the 2017 French Open. The Swiss opens his 15th US Open campaign against a qualifier.
# 2: Marin Cilic (2014 US Open winner)
Marin Cilic is one of five men in the 2019 US Open draw to have won the title at Flushing Meadows. The Croat is also a two-time Grand Slam finalist (2017 Wimbledon and 2018 Australian Open).
Cilic opens his 11th US Open campaign against a qualifier and could face three-time winner Nadal in the fourth round, whom he beat in their last Grand Slam meeting at the 2018 Australian Open quarterfinals.
# 3: Kei Nishikori
The seventh-seeded Nishikori opens his tenth US Open campaign against a qualifier and could face five-time winner Federer in the quarterfinals.
The Japanese is one of seven players in the 2019 US Open draw to have reached the title match at Flushing Meadows. Nishikori lost to Cilic in his only Grand Slam final appearance at the 2014 US Open.
# 4: Roberto Bautista Agut
The newest entrant in the top-ten of the ATP rankings has had a career-best season, winning a title in Doha, beating world no. 1 Djokovic twice, and reaching a maiden Grand Slam semifinal at Wimbledon where he lost to the eventual champion Djokovic.
The tenth seed opens his seventh US Open campaign against Kazakh Mikhail Kukushkin and could face Tsitsipas in the fourth round, Thiem in the quarterfinals and compatriot Nadal in the semis.
# 5: Fabio Fognini
Fognini became the oldest player to triumph at a Masters 1000 tournament when he beat 11-time champion Nadal in the semis and first-time Masters finalist Lajovic in the final in Monte Carlo. Weeks later Fognini became the first Italian player in the top ten of the ATP rankings in over four decades.
The Italian's best performance at a Grand Slam is a quarterfinal appearance at the 2011 French Open. In 11 previous appearances at the US Open, Fognini has gone past the third round only once (2015). That was the year when the Italian overhauled a two-set deficit to upset two-time champion, Rafael Nadal.
Fognini opens his 2019 campaign against big-serving American Reilly Opelka and could face Cincinnati winner Medvedev in the fourth round and defending champion Djokovic in the quarterfinals.
# 6: Nick Kyrgios
The Brisbane and Washington winner is a two-time quarter-finalist at Grand Slams. His most famous win came as a 19-year-old when he stunned two-time winner Nadal at 2014 Wimbledon.
The world no. 29 opens his 7th US Open campaign against American Steve Johnson and could face eighth seed Tsitsipas in the third round, Thiem in the quarterfinals and Nadal in the semis.
The temperamental Australian is not a serious contender for the 2019 US Open title but on his day he has beaten the best players on the grandest of stages.
Who Are Roger Federer's Kids? Know All About Federer's Twins