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.
The 20-year-old Kasatkina, who has beaten all four reigning Grand Slam champions in the past year, continued her giant-killing form with a 6-4, 7-5 shock victory over world No. 2 Wozniacki.
The momentum stayed with Venus and she raced out to a 5-2 lead in the second but struggled to close things out. Then I wouldn't be who I am.
In her first match back, Serena beat Zarina Diyas, the 53rd-ranked player in the world.
Venus Williams turned back time and reached the BNP Paribas Open quarterfinals for the third time in her career.
Typically, the sisters wouldn't meet until the later rounds of a tournament. This led to their boycott of the tournament for more than a decade. Venus recovered well to take the second set 6-3 before Serena made the decisive break to win third set 6-4 to win her first Australian Open title.
Sakkari hired Johansson, the 2002 Australian Open champion, before the US Open previous year and she reached a career-high ranking of 48 a couple of months later.More news: AfDB Partners International Solar Alliance To Deliver Power To 250 Million Africans
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However, she revealed in February that she "almost died" after giving birth and was bedridden for six weeks.
Meanwhile, the 37 year old Venus Williams has leaped to the quarterfinals of the Indian Wells tournament where she will be meeting the 27 seeded Spaniard Carla Suarez Navarro. As always, the game was a match for the ages, and marked the earliest meeting between the sisters in the tournament since way, way back in 1998. Serena (and all mothers) should be protected by the WTA and allowed to use their protected ranking for seeding, if applicable.
But for now, the rule stands and Serena, who will have an official ranking next Monday, will continue to be the most risky unseeded player in women's tennis.
"It's good that I don't have to say that this is the best tennis I have ever played and I lost". But then again, I wish it wasn't. I don't know how long Serena (and Venus, for that matter) has left at the top, but I wouldn't bet against her getting back on track. The match also saw Serena making 41 unforced errors, including 17 on the forehand side. She finished with 41, compared to Venus' 19, and failed to serve her best. It's a little bit of everything that comes in a match that just doesn't normally happen.
However, Venus proved too superior for Serena in the match as the former clinched a comfortable 6-3, 6-4 win over the new-mom in the last-32 clash that lasted one and a half hour.
Wozniacki had a chance to get the No. 1 back but she needed to win the Indian Wells title to do it.
From the first minute, the match was intense, as both players showed pace and precision as they hit the ball.