The luckless South Australian rightly branded his 7-6 (7-5) 4-6 6-3 7-5 victory over the Open's 11th seed and two-time grand slam finalist as his finest yet at a major.
"Massive relief," Kokkinakis said after ousting last year's Australian Open runner-up for only his second ever US Open main-draw win.
"Super happy. Super pumped. It's been well documented I've had some tight ones, but I'm starting to get on the winning end of them now.
"Just a lot of hard work going into it, staying positive and just competing my nuts off."
But the one-time Roger Federer slayer admits making the US Open junior final 11 years ago seems a lifetime ago and, now that he's finally injury-free, says it's high time to start fulfilling his undoubted potential.
"It's gone quick," Kokkinakis said.
"There's that middle period in between in my career for five or six years where I was just pretty much a no-show, trying to get back and couldn't.
"I've never felt like I've played my best tennis here, which is a surprise because it should suit me and my game.
"But I've been training well and (today) I was able to play somewhat close to the level of training."
Robbed of some of his best years, Kokkinakis has endured a cruel run since undergoing shoulder surgery on his right serving arm at Christmas in 2015.
Since then, he has suffered from elbow and knee injuries, lingering osteo pubis, pec issues and torn oblique and abdominal muscles.
"A big thing that I've harped on about is just kind of trying to make the most of whatever I have left," the 28-year-old said.
"I've missed the middle period of my career. When you're younger and you kind of shoot up the rankings pretty quick, you think it's all up."
Kokkinakis knows knocking Tsitsipas out will count for little if he can't back it up against world No.34 Nuno Borges to make the third round and beyond.
"A big part of how impressive these guys are is their consistency to back it up week after week and just give themselves chances to play," he said.
"I've always known I've shown it before that I'm capable of beating good top-10 players.
"It's just trying to be consistent with it."
AUSSIES IN ACTION ON DAY THREE OF THE US OPEN ON WEDNESDAY (THURSDAY AEST):
Men's singles, second round
28-Alexei Popyrin v Pedro Martinez (ESP)
Rinky Hijikata v Grigor Dimitrov (BUL)
Women's singles, second round
Maya Joint v 14-Madison Keys (USA)
Ajla Tomljanovic v 33-Elise Mertens (BEL)
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