(Reuters) - World number one Angelique Kerber was knocked out of the Brisbane International by Elina Svitolina on Thursday while second seed Dominika Cibulkova also succumbed to a quarter-final upset.
Ukrainian sixth seed Svitolina prevailed 6-4 3-6 6-3 in her slugfest with Kerber to set up a semi-final clash with Karolina Pliskova who beat Roberta Vinci 3-6 6-2 6-2.
With Kerber struggling with her serve and rhythm, Svitolina claimed the first set but the German staged a brilliant comeback in the second to force the decider.
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Kerber seemed to have found her range in the third set but Svitolina broke and then served for her second successive win over the top seed.
Earlier, an inspired Alize Cornet pulled off a 6-3 7-5 upset win over Cibulkova to book a last-four battle with Garbine Muguruza who survived yet another grueling contest at the Pat Rafter Arena.
Cibulkova had to toil for her three-set win over China's Shuai Zheng on Tuesday and the Slovakian world number five did not look convincing against Cornet either.
Cornet won the first set without much difficulty and led 5-2 in the second when Cibulkova staged a mini comeback, breaking the unseeded Frenchwoman twice to level at 5-5.
Cornet broke Cibulkova again for 6-5 and served it out on her third attempt.
"What a start of the year! It's the first week and I think my game is not so bad," Cornet said.
"Beating a player like Dominika takes an amazing performance, everybody knows how much she fights and hits the ball hard."
Muguruza had survived tough three-setters against Sam Stosur and Daria Kasatkina in her previous two matches and the Spaniard dug deep to beat Russian Svetlana Kuznetsova 7-5 6-4.
Kuznetsova dictated early terms with her heavy forehand to race to a 4-1 lead, prompting Muguruza into a huddle with her coach.
Muguruza changed strategy after the pep talk and tried to keep points shorter. The ploy worked as she reeled off three games to level at 4-4.
Muguruza went on to save two set points to claim the first set and broke Kuznetsova twice in the second to advance to the last four.
(Reporting by Amlan Chakraborty in New Delhi; Editing by Clare Fallon)