The Japanese became the youngest player in nine years to triumph at the BNP Paribas Open in Indian Wells last weekend, and she had carried her excellent form into the second half of the sunshine double.
Osaka previous stated that her was aim to tackle Maria Sharapova and the Williams sisters during her career – and she has now notched victories over all three multiple Grand Slam champions.
Williams, an eight-time winner in Miami, must have been cursing her luck when the draw pitted her against a confident young upstart, but in truth, she would have struggled against the majority of the Top 30 based on today’s performance.
The 36-year-old, still trying to find her rhythm after more than a year out, was untidy from the baseline and not much went in her favour throughout the standout tie of the round.
It was Williams who carved open the first break-point opportunity in the first set – but Osaka managed to avoid danger with a booming first serve. The Japanese then created a 0-40 scenario on her opponent’s delivery in the seventh game, and she was not to be denied.
The American got caught in a difficult position and yanked a backhand wide to fall 4-3 behind. There was further disappointment for the crowd-favourite when she pulled a forehand wide to lose a fourth game in succession.
Osaka, assisted by her impressive serve, pocketed the opener convincingly and was soon in control of the second set. Williams dumped a backhand in the net to slip 3-1 behind and she grew increasingly exacerbated at her inability to keep the ball within the confines of the court.
At no stage did the American look likely to reduce the arrears – and she nudged a simple forehand beyond the baseline while facing match-point. It was a glaring miss that further compounded her misery, and she has much to ponder ahead of the upcoming clay-court season.
Osaka's second round assingment will also be a tough test. The 20-year-old will encounter Elina Svitolina later this week.
Earlier in the day, Victroria Azarenka opened up her campaign in impressive fashion. The Belarusian enjoyed a comprehensive 6-3 6-0 success over Catherine Bellis in just 66 minutes.