His unlikely emergence led commentator Nick McCarvel, who calls the action from Melbourne Park for a feed that is distributed across the globe, to admit he'd never heard of the 27-year-old before this year.
But his admission of ignorance has been poorly received by world number 200 Sergiy Stakhovsky.
"This is exactly why our sport is suffering," Stakhovsky replied to McCarvel's tweet. "And he is supposed to be a commentator."
Several of the world's tennis media leapt to McCarvel's defence, sparking a petty exchange.
"If I may, a commentator hired to cover a Grand Slam isn't going to automatically know every player that has never played a Grand Slam main draw, like Karatsev," the BBC's David Law said. "But they can find out. And he found out. I've watched (McCarvel's) commentary this fortnight. It's been very good."
"Then I guess you are not doing your job properly," Stakhovsky replied. "And there are not many excuses you can come up with. Last year there were not tournaments to follow, and he rocked those few. Guess you guys are comfortable with glorifying the top 4."
New York Times tennis correspondent Ben Rothenberg then jumped in.
"Stakhovsky has used this long thread to gripe about people having never heard of a guy who had never played a Slam main draw, instead of, you know, telling us anything about him to make us care and enrich his story," he wrote. "Tennis players are so dang bad at selling their sport/peers."
"Don't remember inviting Ben to this thread… did someone else?" Stakhosvky responded.
"I don't remember anyone inviting you to s*** on Nick McCarvel, who is so much more 'professional' than you've ever been," Rothenberg replied.
So much for the happy slam.
Osaka dominates veteran rival
In the first quarter-final singles contest of the Australian Open, three-time grand slam champion Naomi Osaka faced Taiwanese veteran Hsieh Su-wei.
Osaka broke first in the opening set, unforced errors coming few and far between for the Japanese powerhouse.
Hsieh had an opportunity to put the first set back on serve, but failed to convert the break point at 3-1.
The 23-year-old Osaka then emphatically claimed the opening set in 37 minutes by breaking serve at 5-2. Hsieh made 15 unforced errors in the first set.
Hsieh's run of unforced errors continued through to the second set as Osaka immediately took a 3-0 lead.
Although Hsieh managed to take Osaka's next service game to deuce, the Japanese star held her nerve.
Down 5-2 in the second set, Hsieh managed to save two match points to keep the contest alive, but Osaka made no mistakes when the third chance came.
An Osaka victory seemed inevitable, particularly when considering every time she has advanced beyond the fourth round of a grand slam tournament, she's gone on to claim the title.
"I'm really happy with how I played today too," Osaka said after the straight sets win.
"Every time I play her, it is always such a battle. Even though the score was like this, it was really another battle for me."
Sports reporter Meredith Cash tweeted: "Clinical performance from Osaka. On to the next."
Osaka will face either American icon Serena Williams or world No. 2 Simona Halep in the semi-finals.
Playing in her 38th grand slam tournament, this is the first time the 35-year-old Hsieh has qualified for the quarter-finals of a major.
