Seven-time Grand Slam champion Serena E.S. Williams, 37, was winning matches at Indian Wells before Daria S. Kasatkina had even been born, but was worn down by the youngster, who broke her seven times. Photo: Reuters/File

Haitian-Japanese tennis player Naomi Osaka reached a career-high ranking of 40th in 2016. Photo: Reuters

20-year-old Kasatkina beat world number eight Williams 4-6 6-4 7-5.

It was the Russian's fourth consecutive victory over a current top-20 player, all of whom have won Grand Slams, according to BBC Sport.

World number 19 Kasatkina overcame 2017 US Open champion Sloane Stephens in the third round, before beating January's Australian Open winner and world number two Caroline Wozniacki.

Then, in the last eight, she knocked out world number 10 Angelique Kerber, who won both the Australian and US titles in 2016.

"[After a] match like this, you're just speechless," she said. "Too many emotions and you cannot explain everything. It's one of the best nights in my life, for sure."

Too many errors

Seven-time Grand Slam champion Williams, 37, was winning matches at Indian Wells before Kasatkina had even been born, but was worn down by the youngster, who broke her seven times.

After the pair traded the opening two sets, Williams eked out a 5-4 lead in the third after around two and a half hours of play but was left breathing heavily in her chair.

Kasatkina responded, winning the final three games and clinching the win on her second match point after two hours 49 minutes.

"Anyone who gets used to losses should give up on life," said Williams, who beat sister Serena in the third round. "I have to stop making that many errors against her."

Osaka, meanwhile, has taken her share of big-name scalps in California, knocking out Maria Sharapova, Agnieszka Radwanska, Karolina Pliskova and now Halep.

The unseeded Osaka, ranked 44 in the world, thrashed lacklustre world number one Halep 6-3 6-0 in 64 minutes.