Maria Sharapova, the 2006 champion who was trying to reach the quarter-finals for the first time since 2012, hit 38 unforced errors and dropped serve six times
Maria Sharapova was knocked out of the US Open in the fourth round on Monday, losing 6-4, 6-3 to Spanish birthday girl Carla Suarez Navarro who inflicted the Russian's first ever night-time loss at the tournament.
Sharapova, the 2006 champion who was trying to reach the quarter-finals for the first time since 2012, hit 38 unforced errors and dropped serve six times.
The defeat ended the former world number one's perfect record of 23 wins -- 22 of them on Arthur Ashe Stadium -- in night sessions at Flushing Meadows.
Suarez Navarro, who celebrated her 30th birthday Monday, was a quarter-finalist in New York in 2013.
"Maria has played here at night many times so I knew I needed to be aggressive, focussed and play solid," said the 30th seeded Spaniard after clinching a second win in six meetings with Sharapova.
"I told myself to run and fight -- that's the way I can play really good tennis."
She will face 2017 runner-up Madison Keys for a place in the semi-finals.
"Madison is from the United States so I guess all the crowd will be for her.
"I have played her a few times. She has a great serve and plenty of experience on this court."
Sharapova, who won the last of her five Slams at Roland Garros in 2014, has endured a disappointing return to the majors since the end of her drugs ban in April of 2017.
She made the fourth round in New York last year, third round in Australia in January, quarter-finals in Paris before a first round exit at Wimbledon.
Her loss to Russia's Vitalia Diatchenko, the world number 132 at the time, at the All England Club was her first opening round Wimbledon defeat and earliest Grand Slam exit in eight years.
"I definitely expected more from the Slams this year," said the 31-year-old.
"But I have the motivation and belief every day to continue."
Keys made the last-eight with a 6-1, 6-3 win over Dominika Cibulkova.
The other quarter-final in the bottom part of the draw will see Japan's Naomi Osaka face Lesia Tsurenko of Ukraine.
Osaka, the 20th seed, made the last-eight of a major for the first time by beating Aryna Sabalenka of Belarus 6-3, 2-6, 6-4.
Tsurenko also made sure of a maiden quarter-final at the Slams by seeing off Czech teenager Marketa Vondrousova.
Eighteen of Sharapova's unforced errors came in an untidy first set where she trailed 1-4 and 2-5.
In the second set, she retrieved a break for 1-1 but dropped serve again in the fifth and ninth games with her fate sealed by a wild backhand.
Osaka reached her first Grand Slam quarter-final, tearfully admitting she was prepared to "break a leg" to win the match.
The 20-year-old became the first Japanese woman in the US Open last-eight since Shinobu Asagoe in 2004.
Osaka, seeded 20, came back from a break down in the final set to take the tie on a fourth match point when Sabalenka served up an eighth double fault.
"I would never have forgiven myself if I had lost that match," said a tearful Osaka.
"When I was a break down in the final set I thought I would even break a leg if needed so I could get to every ball."
Tsurenko, 29, had been on the brink of collapse due to heat exhaustion before seeing off Vondrousova.
World number 36 Tsurenko was a set and 0-2 down when she bent double on the sizzling Grandstand court, looking increasingly unsteady in the 33-degree heat and crushing humidity.
"I was really dizzy and I asked nature or God or somebody please move the shade over faster," said the woman who put out world number two Caroline Wozniacki in the second round.
In the two-hour 32-minute match, which featured 13 breaks of serve, Tsurenko committed 57 unforced errors while 19-year-old Vondrousova hit a huge 73.
The Czech world number 103 thought that Tsurenko was exaggerating her distress.
"I was angry. It was weird because she called the doctor and then she was playing normally. I don't get it," she said.
The two other quarter-finals will feature six-time champion Serena Williams against Karolina Pliskova, the Czech eighth seed, while third seed Stephens faces Latvia's Anastasija Sevastova.