German qualifier Jule Niemeier defeated defending champion Ons Jabeur 7-6 (4), 6-4 in the first round of the Berlin Open on Tuesday.
Niemeier, ranked 120th in the world, saved two set points at 5-3 down in the first set and then won the last four points of the tiebreak. Niemeier broke Jabeur in the first game of the second set and held her lead to win in 1 hour 35 minutes for the 23-year-old’s third win against a top 10 player.
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Coco Gauff defeated Czech player Katerina Siniakov 6-3, 6-4 for the American teenager’s 23rd win of the year.
The fourth-seeded Gauff next faces heavy hitter Ekaterina Alexandrova, who defeated fellow Russian Liudmila Samsonova 6-4, 6-3.
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Top seed Aryna Sabalenka advanced to the second round with a 6-3, 6-2 victory over veteran Vera Zvonareva in another all-Russian match.
Sabalenka converted three of her nine break points without facing any of Zvonareva, 38, a 2010 Wimbledon finalist.
Sabalenka now faces Veronika Kudermetova or Zheng Qinwen.
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Elina Avanesyan saved two match points and defeated sixth seed Daria Kasatkina with a 6-2, 3-6, 7-6(7) win to take on fellow Russian Anna Blinkova.