INDIAN WELLS - Unseeded Katerina Siniakova ended Mirra Andreeva's Indian Wells title defense on Monday, rallying for a 4-6, 7-6 (7/5) 6-3 victory over the eighth-ranked Russian.
The 18-year-old Andreeva had opened her repeat bid with an imperious 6-0, 6-0 demolition of Solana Sierra.
But she was in trouble early and often against 44th-ranked Siniakova in a rollercoaster contest that ended with a shot from Siniakova that hit the net cord and dribbled over in one last frustrating moment.
The 18-year-old Russian slung her racquet as she approached the net before departing the court with a defiant gesture at the censorious crowd.
Siniakova, a former doubles number one, admitted it was an awkward way to seal the win in a match that featured seven service breaks for each player and 43 break chances between them.
"Of course I'm happy it went on the other side," she said. "I was, like, should I cheer? It's a really tricky finish. But definitely I will not say I'm not happy."
Siniakova said the swirling winds on Stadium Court were troubling both players.
Andreeva's emotions had already boiled over when she sailed a swinging volley long to surrender the second set, during which each player had remarks for the chair umpire about her opponent.
She regrouped to break Siniakova for a 3-2 lead in the third, but Siniakova won the next four games, saving two break points in the final game before gaining the win on her first match point.
Siniakova will face Elina Svitolina for a place in the quarter-finals after the ninth-seeded Ukrainian beat American Ashlyn Krueger 6-4, 6-2.