Kyrgios, the 14th seed who was the highest-ranked obstacle in Roger Federer's path to the quarter-finals, lost to 235th-ranked compatriot John Millman 6-3, 1-6, 6-4, 6-1.

"I know in the back of my mind Nick's shoulder deteriorated as the match went on," Millman said after his first US Open triumph. "It's a victory but slightly hollow.

"He's a teammate. He's a great guy on and off the court. I feel for him. I really do."

Kyrgios endured an injury-nagged run-up to the US Open, hip pain knocking him out of Wimbledon and Queen's and a sore right shoulder forcing him out at Washington.
 
But he rolled to the ATP Cincinnati Masters final two weeks ago, falling to Grigor Dimitrov.

The 22-year-old Aussie, known for outspoken remarks and often doubting his desire to play tennis, was in strong form when he grabbed his elbow of his first serve of the fourth game in the third set.

After having a ballboy grab his right arm between games to try and relieve the pain, Kyrgios had treatment by a physiotherapist during a timeout and told him his troubles.

"One serve and arm is totally dead. It's so dead and numb. It's incredibly weak," said Kyrgios. "How can something happen all of a sudden? I wasn't feeling it at all and then Bang, one serve. I lost power in my serve."

Frustration grew as Kyrgios screamed an obscenity while glaring at his right hand after slamming down a racquet following the fifth game.
"My forehand is painful. It's so annoying," Kyrgios told the trainer after a line change.

Kyrgios grimaced during a treatment sessions, saying, "I try hard and then one serve I can feel it. I don't get it. I don't know what to do."

"I'm feeling good. I finally have a good week last week, come to the US Open feeling good, playing a good match against an Aussie, third set and it's throbbing."

After his last available treatment, Kyrgios was broken to drop the set, sending a forehand wide on the decisive point then smashing his racquet on the court.

He was docked a point for that transgression.

Millman, who missed nearly eight months with a hip injury, dominated the final set to send Kyrgios home.
                  
- Thiem, Svitolina advance -                  
                  
In other matches postponed from Tuesday by rain, Ukraine's fourth-seeded Elina Svitolina, fighting to become world number one, and Austrian sixth seed Dominic Thiem advanced.

Svitolina, seeking her sixth title of the year and first Grand Slam crown, held off 42nd-ranked Czech Katerina Siniakova 6-0, 6-7 (5/7), 6-3 while Thiem finished off Australian Alex de Minaur 6-4, 6-1, 6-1.

Thiem, a semi-finalist at the past two French Opens, is the highest-ranked rival on the same side of the draw as favorites Federer and Rafael Nadal.
"I'm not in the first row of favorites, maybe in the second, so I can play calm," Thiem said.

Former world number one Maria Sharapova, who in her Grand Slam return from a 15-month doping ban upset second-ranked Simona Halep, was set to face Hungary's 59th-ranked Timea Babos in a later second-round match at Arthur Ashe Stadium.

Sharapova, a five-time Grand Slam champion, tested positive for blood booster meldonium in the 2016 Australian Open, her most recent Grand Slam appearance until this week. 

She played only one hardcourt tuneup match due to a forearm injury but powered past one of seven contenders for the world number one ranking still in the field.

Another of those is Svitolina, who dropped six of nine tie-breaker points when her match resumed but battled into the second round.
"It was a little bit unlucky to stop because I was playing good," Svitolina said. 

"Today was a little bit of a mess in my head. It was tough to keep my focus. I'm happy I could win the third set and play really good tennis.
"I was just trying to fight for every ball. You can't win if you're not mentally strong."