Kostyuk stretched US Open champion Coco Gauff for three hours and seven minutes before finally succumbing 7-6 (8-6) 6-7 (3-7) 6-2 to the fourth seed in a Melbourne Park thriller on Tuesday.
As well as battling blisters and searing heat, the 21-year-old is enduring the ongoing war in her homeland where her sister and parents remain stranded as Russia rain down bombs on Ukraine seemingly each and every day.
Kostyuk has used her Open campaign to shine the light on Ukraine's plight and questioned why Russian and Belarusian players were even allowed to compete at the tournament.
The world No.37 showed similar resolve against Gauff and shrugged "it's just a tennis match" after bowing out.
"I'm here to grow, to learn, to be better. Yeah, very proud of myself. I won for myself today, and it's the most important thing," Kostyuk said.
"It's just the beginning of the season. Looking forward for what's ahead."
After blowing the opening set from 5-1 up, Kostyuk left Melbourne Park feeling like a winner because of the way she managed to fight back from 5-3 down in the second to force a decider.
"I was playing one of the best girls in the world. Managed to be still very close," she said.
"It feels far but also very close. This whole tournament was a big win for me."
Asked what her biggest take-away was, Kostyuk said: "The first one is dream big".
"Because I started the season I knew I'm doing the right things and I knew I'm working well. Everything is kind of aligning.
"I still want to win a grand slam. It's still my biggest goal. I will be going for that.
"There were a lot of things I just went through in this last 10 days, and it was from not being able to fall asleep then to really barely lifting my leg in fourth round.
"I really felt like it's easier to cut my leg off because it (the blisters) was really, really painful.
"The team here was amazing. The physios and massage therapists, they just brought me back to life somehow.
"I was still in a lot of pain most of the tournament and I still managed to compete and show a great level of tennis.
"So there is really no limit in human possibilities."
Just as the people of Ukraine are showing, and that's what matters most to Kostyuk that the world knows her country is still under invasion.
"People should be reminded," she said.
"When I walked off the court I look at this news again and again, I don't know how many missiles yet. It's still too fresh.
"But I was texting with some people from Kiev. 'How is it? How are you guys?'
"They said, 'Well, we were looking between your score and where the missiles are flying'.
"So it's still there. My parents are still there. It (the war) is not gone.
"If someone would have told us like one month after the war began that this would last for two years, I think everyone would just die.
"Literally just say, 'No, never, we will never withstand it, we will never survive this for two years'.
"It's very exhausting to live in this state.
"It's incredibly difficult, but everyone is hanging very tight."
