Kasatkina hasn't enjoyed the best of results since she officially switched allegiance from Russia to become Australia's No.1 in March, while admitting that all the hoopla surrounding her new citizenship may have impacted her on-court performances.
Since the switch, the eight-time title winner has not reached the last-eight of any tournament - a distinct blip for such a consistent performer who began her new career as an Aussie ranked 12th in the world.
Next week, Kasatkina will drop to No.20 in the world, her lowest position in the rankings since May 2022, after her disappointing 7-6 (7-2) 6-2 defeat on Friday to Czech Katerina Siniakova in the last-16 of the Korea Open.
That makes it 13 consecutive tournaments since she announced the switch where Kasatkina has failed to reach a quarter-final, and she hasn't made the last-eight in any event since the start of the year at the Adelaide International.
That's a veritable drought for a player who reached the last-eight on eight occasions in 2024 and reached four finals, including two tournament wins.
The 28-year-old cut a picture of frustration on Friday. She had dragged herself back into the first set after going 5-2 down, only to then be outgunned again by qualifier Siniakova in a one-sided tiebreak, where Kasatkina was reduced to swishing her racquet against the ground in irritation at her erratic form.
She ended up delivering eight double faults as the 29-year-old Czech doubles specialist Siniakova pulled away in the second set to win in one hour 57 minutes, continuing a brilliant tournament in which she's come through qualifying and won four matches without dropping a set.
Siniakova has also reunited with her old partner Barbora Krejcikova for a doubles appearance in Seoul, with the eight-time grand slam champs so far having eased into the quarter-finals together.
But they could be on course to meet in the singles too after Krejcikova saved three match points before sinking Britain's Emma Raducanu 4-6 7-6 (12-10) 6-1 in the last-16 to set up a last-eight clash with top seed Iga Swiatek.
It left Maya Joint as the last Australian standing in the tournament. The teenager will play Denmark's Clara Tauson in the quarter-finals on Friday.
Elsewhere on the Asian hardcourt swing, it wasn't a great day either for Australian Jordan Thompson in the Chengdu Open in China.
Coming off his exertions during the Davis Cup defeat to Belgium, Thompson, who's down at his lowest ranking at No.78 since June 2023, succumbed 6-3 6-4 in the last-16 to Chilean qualifier Alejandro Tabilo, who broke the Sydneysider's serve once in either set to eke out victory in 80 minutes.
14°C