Naomi Osaka defeated 23-times grand slam singles champion Serena Williams 6-3, 6-2 in the Miami Open first round on Wednesday, the latest big win for the emerging 20-year-old Japanese player.

The pair were on serve in the first set of their first career meeting until Osaka, who won her first career title at Indian Wells last week, forced break point chances at 3-3 and Williams was unable to deal with a blistering backhand at her feet. The world No22 broke Williams again after a back-and-forth deuce battle to take the first set.

Osaka’s powerful serving and relentless return game were even stronger in the second and she broke Williams to go 3-1 up and was never threatened again. The match ended on an ugly unforced error by Williams, who hit a wide open forehand long to send Osaka into the second round, where she will face world No4 Elina Svitolina of Ukraine.

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“I was extremely nervous coming on to the court. I don’t know if anybody knows this but Serena is my favorite player,” Osaka said in an on-court interview. “So just playing against her is kind of like a dream for me. I’m very grateful I was able to play her and it is even better that I was able to win.”

The 36-year-old Williams, playing her fourth match since the birth of her first child in September, is still working her way into form and although she showed her trademark power, she struggled to move smoothly around the court.

Some felt it was unfair that the Miami Open allowed Williams, an eight-times champion at the tournament, to play Osaka in the first round. “Serena should have a special seeding, but also WTA should use the most current ranking,former world No1 Lindsay Davenport said on the Tennis Channel. “The men do it. It’s too big a tournament to have something like this happen.”

Osaka’s win over Williams was her latest victory over some of the biggest names in the sport. She defeated Maria Sharapova, fifth seed Karolina Pliskova and world No1 Simona Halep in Indian Wells.