Roger Federer's run at the US Open came to a stunning end on Monday night -- well, technically early Tuesday morning -- as the tournament's No. 2 seed was bounced at the hands of Australian John Millman. 

Millman took down Federer in four sets, winning 3-6, 7-5, 7-6 (7), 7-6 (3). It was Millman's first career win against a top-10 opponent, and Federer's first loss to an opponent ranked outside the ATP Top 50 (Millman is ranked No. 55). Federer was previously 40-0 against opponents outside of the Top 50.

Federer was clearly not his best self during the match, committing a slew of unforced errors against the 29-year-old Millman. Federer committed 10 double faults during the shocking upset -- the fourth time he's done that in his Major career, and the first time since 2009.

Millman will move on to the quarterfinals to face Novak Djokovic, who did his part Monday as he punched his ticket with a 6-3, 6-4, 6-3 win over unseeded Joao Sosa.

Djokovic, the No. 6 seed in the men's draw, is 28-0 at the US Open when facing an opponent ranked outside the Top 50. Coming off his triumph at Wimbledon, he has reached the final eight at Flushing Meadows for the 11th time. 

Elsewhere in the men's bracket, No. 7 seed Marin Cilic moves on to meet No. 21 seed Kei Nishikori in a quarterfinal. Cilic defeated No. 10 seed David Goffin pretty handily in their match on Monday, taking down Goffin in three straight sets.

In the women's draw, Maria Sharapova was delivered a surprising upset at the hands of Spain's Carla Suárez Navarro. No. 30 seed Navarro defeated 22nd-seeded Sharapova 6-4, 6-3. The big win for Navarro comes on her 30th birthday. She took six of eight break points.

For Sharapova, it's her first loss at night at the US Open, moving her to 23-1 all-time under the lights at the Open.

No. 14 seed Madison Keys remains in the hunt for her first Grand Slam title a year after making the US Open final. Keys punched her ticket to the quarterfinals with a dominant 6-1, 6-3 victory over No. 35 seed Dominika Cibulkova of Slovakia.

Keys lost to Sloane Stephens in last year's final, and also lost to Stephens again this year in the French Open semifinals. She moves on to face Navarro.

Keys, who has made at least the quarterfinals in three of the four Grand Slams this year, fired six aces and had no double faults to dispatch Cibulkova in short order.

Naomi Osaka also reached the quarterfinals with a 6-3, 2-6, 6-4 win over Aryna Sabalenka, becoming the first Japanese woman to make the final eight at a Grand Slam in 14 years. Osaka had won 22 consecutive games leading into the match, but was tested by Sabalenka, who double-faulted on match point. 

Osaka will meet Lesia Tsurenko in the quarterfinals. Tsurenko took down Markéta Vondroušová in three sets on Monday.

Here's Monday's results:

Men's matches

  • No. 21 Kei Nishikori defeats Philipp Kohlschreiber 6-3, 6-2, 7-5 
  • No. 6 Novak Djokovic defeats Joao Sousa 6-3, 6-4, 6-3
  • John Millman defeats No. 2 Roger Federer 3-6, 7-5, 7-6, 7-6
  • No. 7 Marin Cilic vs. No. 10 David Goffin 7-6, 6-2, 6-4

Women's matches

  • No. 14 Madison Keys defeats No. 35 Dominika Cibulkova 6-1, 6-3
  • No. 20 Naomi Osaka defeats No. 26 Aryna Sabalenka 6-3, 2-6, 6-4
  • No. 30 Carla Suárez Navarro defeats No. 22 Maria Sharapova 6-4, 6-3 
  • Lesia Tsurenko defeats Markéta Vondroušová  6-7, 7-5, 6-2