Indian Wells - Russian Daria Kasatkina, who has beaten all four reigning Grand Slam champions in the past year, upset world No 2 Caroline Wozniacki 6-4, 7-5 at the WTA Indian Wells event on Tuesday.
Kasatkina recorded her second straight win over Wozniacki, having also beaten the reigning Australian Open champ at the St. Petersburg tournament last month.
The 20-year-old Kasatkina improved to 11-6 on the WTA Tour season as she seeks to better her quarter-final appearance here in 2016.
Kasatkina hit one ace, won 54 percent of her first serves and broke Wozniacki's serve six times in the one hour, 40 minute match.
"She outsmarted me today, which is fair enough," Wozniacki said. "But, you know, at least I tried, and I tried to do what I thought I needed to do out there today.
"I just couldn't execute as well as I wanted to."
It was a disappointing exit for Wozniacki, who finally silenced her critics earlier this year with her maiden Grand Slam title in Melbourne, where she defeated Simona Halep in the final.
That victory not only earned Wozniacki her first Grand Slam title but it made her the world number one. Halep reclaimed the ranking just before Indian Wells.
Wozniacki had a chance to take it back but she needed to win the Indian Wells title to do it.
Kasatkina will play either seventh seed Caroline Garcia of France or Angelique Kerber of Germany in the quarter-finals.
Results on Tuesday on the seventh day of the ATP and WTA Indian Wells tournament:
Feliciano Lopez (ESP x28) bt Jack Sock (USA x8) 7-6 (8/6), 4-6, 6-4
Sam Querrey (USA x18) bt Yuki Bhambri (IND) 6-7 (4/7), 6-4, 6-4
Marcos Baghdatis (CYP) bt Dudi Sela (ISR) 7-6 (7/5), 6-4
Milos Raonic (CAN x32) bt Joao Sousa (POR) 7-5, 4-6, 6-2
Juan Martin Del Potro (ARG x6) bt David Ferrer (ESP x29) 6-4, 7-6 (7/3)
Leonardo Mayer (ARG) bt Taro Daniel (JPN) 6-4, 6-1
Pierre-Hugues Herbert (FRA) bt Gael Monfils (FRA) 6-2, 3-1 retired
Philipp Kohlschreiber (GER x31) bt Marin Cilic (CRO x2) 6-4, 6-4
Simona Halep (ROM x1) bt Wang Qiang (CHN) 7-5, 6-1
Petra Martic (CRO) bt Marketa Vondrousova (CZE) 6-3, 7-6 (7/4)
Naomi Osaka (JPN) bt Maria Sakkari (GRE) 6-1, 5-7, 6-1
Karolna Pliskova (CZE x5) bt Amanda Anisimova (USA) 6-1, 7-6 (7/2)
Venus Williams (USA x8) bt Anastasija Sevastova (LAT x21) 7-6 (8/6), 6-4
Carla Suarez Navarro (ESP x27) bt Danielle Collins (USA) 6-2, 6-4
Darya Kasatkina (RUS x20) bt Caroline Wozniacki (DEN x2) 6-4, 7-5