New York, NY, USA, 31 August 2017 | Darren Walton (AAP)

John Millman is cherishing, if not celebrating, one of the most significant wins of his career after cashing in on Nick Kyrgios’s physical frailties to storm into the second round of the US Open for the first time.

Playing on an injury-protected ranking of his own, Millman kept his nerve as Kyrgios battled his box, officials and ultimately a wounded shoulder to carve out a bittersweet 6-3 1-6 6-4 6-1 victory over his more-fancied countryman.

“It’s a victory, but a hollow victory,” Millman said.

“I know in the back on my mind his shoulder deteriorated as the match went on. He’s a teammate. I feel for him, I really do.”

Kyrgios earned two code violations – one for swearing and one for obliterating his racquet after dropping the third set, the latter costing him a mandatory point penalty to start the fourth set.

There was no way back as the 14th seed surrendered the match after two hours and 15 minutes.

Millman said facing Kyrgios made life difficult.

“It’s even tougher when you’re playing against a fellow countryman,” he said.

“Davis Cup’s around the corner and all of Australia is hoping he’s fit in time for that and it does make it that little bit tricky.

“Even as the match progressed and his shoulder was causing him grief, he was sending down 136-mile-an-hour rockets. It’s really tricky.

“You’ve got to try to stay focused and take those little half chances.

“There’s no doubt he’s talented enough, even if he’s not at 100 per cent, to kind of just slap a few shots and really take control.”

Millman’s victory set up a second-round shot at Tunisia’s Malek Jaziri.

Kyrgios hopes the returning world No.235 can take advantage of his breakthrough.

“He’s always been pretty nice to me. John,” he said.

“I know he’s obviously had some physical struggles, as well, had shoulder surgery. He’s been struggling over the last year or two. I get happy when I see someone like that that’s been through a lot.

“He’s got a good opportunity. Obviously the draw opens up for him now. God knows where he could be in a couple of days if he competes.”