Top seed Aryna Sabalenka crashed out of the WTA Finals in Guadalajara on Monday, losing a grueling three-setter against Greek fourth seed Maria Sakkari.
Sakkari set up a semi-final showdown with Estonia's Anett Kontaveit after outlasting Sabalenka 7-6 (7/1), 6-7 (6/8), 6-3 in 2hr 47min.
Sabalenka was left ruing a failure to capitalise on key moments and an eye-watering 19 double faults that undermined her service game.
The 23-year-old Belarussian squandered the chance to take the lead in the first set, allowing Sakkari to recover from 3-5 down to force a tiebreak.
Sakkari then raced through the tiebreak to win 7/1, leaving Sabalenka needing to win the next two sets to stay alive in the tournament.
The top seed managed to dig deep to take the second set on a tie break after once again letting Sakkari back into the game to come back from 5-3 down to 5-5.
But a weary Sabalenka wilted in the decisive third set, making 10 double faults to win less than half of her first-serve points.
Sakkari, 26, is chasing only her second WTA title after a win at the Morocco Open in 2019.
The right-hander is competing at the end-of-season women's championships in Mexico after a 2021 campaign that included semi-final appearances at the French Open and US Open.
The other semi-final will see Spain's Paula Badosa take on compatriot Garbine Muguruza, also on Tuesday.
Badosa, who was already assured of a place in the semi-finals, wrapped up her group stage with a 5-7, 4-6 loss to already-eliminated Iga Swiatek of Poland.
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