Australian John Millman has stunned young gun and countryman, Nick Kyrgios, knocking him out of the US Open in four sets.

Kyrgios, who prior to the tournament had been in blistering form, reaching the final of the Cincinnati Masters let his temper get the better of him in the 6-3 1-6 6-4 6-1 loss, before yet another bizarre post-match press-match press conference, in which he revealed he is "not dedicated to the game at all".

The 22-year-old also complained of a "dead" shoulder during the match.

“I don't know, honestly. I'm not good enough for him,” Kyrgios said when asked if he would continue working with coach Sebastian Grosjean.

“He's very dedicated. He's an unbelievable coach. He probably deserves a player that is probably more dedicated to the game than I am. He deserves a better athlete than me.

“I'm not dedicated to the game at all.

“He's helped me a lot, especially with the training, in training sessions, but there are players out there that are more dedicated, that want to get better, that strive to get better every day, (do the) the one-percenters. I'm not that guy.

“I have had a diabolical year at these slams. It doesn't surprise me,” he said. “It's just the story of my career, really. I will have good weeks; I'll have bad weeks. It's just a rollercoaster.”

Kyrgios said he is at a loss to explain how or why he suffers such capitulations.

“In Cincinnati, I was not doing anything different. I was probably less dedicated than I was this week,” Kyrgios said.

“I was playing basketball at Lifetime Fitness every day for two hours. Like I played an hour of basketball before I played David Ferrer in the semi-final.

“I was going to ice cream, like this Graeter's place getting a milkshake every day. I was less dedicated.

“And this week I was dedicated, and my shoulder starts hurting. I don't know.

“I don't know. I don't know. I keep letting people down."

Kyrgios has had a horrid run at grand slams this year, winning just two matches.

Millman will next face Tunisian Malek Jaziri in the second round.