Along with the boilovers created by Adam Walton and Kim Birrell and one wholly improbable comeback win by the luckless Thanasi Kokkinakis, Kasatkina's resurgence after her troubled year has been one of the real bonuses of a tough Aussie week at Roland Garros.
She made it to Saturday as the last Australian standing at the French Open for the second successive year, after Alex de Minaur's desperately disappointing capitulation to Jakub Mensik, also in the third round, the day earlier.
But an outing against the four-time grand slam champion Sabalenka on Court Suzanne Lenglen always shaped to be a fight too far for the country's most high profile tennis import as Kasatkina battled in vain before falling 6-0 7-5.
But after a tough spell in her career since swapping her allegiance to Australia last year, the 29-year-old admitted her recent on-court resurgence, capped by a victory in a minor tournament in Spain two weeks ago and a couple of wins here in Paris, had quite transformed her mood.
"I can only take the positive out of the clay-court season, because the position I was in before was pretty bad, honestly."
How bad? On a scale of one to 10? "I was before 2 — where 1 is 'I want to kill myself!'," laughed Kasatkina. "Now how I feel about myself on court, I would say 'between 6 and 7'.
"I feel way better than I felt a couple of months ago."
On the last day of the seven-day heatwave before temperatures are forecast to plummet significantly on Sunday, Kasatkina had promised to take the fight to the Belarusian but Sabalenka, who went in holding a 7-2 head-to-head advantage, began with the sort of searing form that matched the weather.
The last time they'd met at Roland Garros six years ago when Kasatkina was competing as a Russian, the match had ended with Sabalenka whitewashing her friendly foe with a 6-0 set.
She began as if they'd just left off, seemingly hammering winners at will -- 16 in all in the first set -- as the 29-year-old Australian simply couldn't cope with the irresistible power and accuracy.
But Sabalenka had expected a fight from a clever all-court player she'd described as "amazing" and she got one in the second stanza, the world No.53 Kasatkina breaking her duck and the Belarusian's serve to move into a 2-0 lead.
It was fleeting, though, as Sabalenka immediately hit back and then held the initiative, only for Kasatkina to use all her wiles to stay in the hunt.
At 5-5, she looked to have a glimmer of a chance at 0-30 when her loopy forehand returns caused some concern for last year's finalist, but Sabalenka regrouped, and then got lucky at the start of the fateful final game.
The top seed got a net cord that plopped over stone dead, and then Kasatkina double-faulted, paving the way for Sabalenka to smash a 37th winner en route to a 76-minute win, her 100th as a world No.1, and a blockbuster last-16 meeting with Naomi Osaka.
