Serena Williams tumbled out of the Miami Open yesterday after a straight-sets defeat to Indian Wells champion Naomi Osaka.
The Japanese went all the way in last week's BNP Paribas Open, defeating Maria Sharapova and world number one Simona Halep along the way, and she added Williams' scalp in supreme style.
The 20-year-old was dominant from the off and clinched a 6-3 6-2 victory over the 23-time grand slam champion in 78 minutes.
Williams was playing in just her second event since returning to the tour after giving birth to her daughter last September.
Three-time Miami Open champion Victoria Azarenka, playing just her fourth event since the birth of her son, claimed a 6-3 6-0 win over American Cici Bellis.
Azarenka, the winner in 2009, 2011 and 2016, dispatched the 18-year-old in just over an hour.
Bethanie Mattek-Sands was beaten in her first competitive outing on the WTA Tour since a horror fall at Wimbledon last year.
The American had been sidelined since dislocating her right kneecap and rupturing a tendon when her leg buckled during her second round singles match against Sorana Cirstea at SW19 last July.
The 32-year-old doubles specialist was unable to make a winning return, having been given a wild card spot in Miami, as she went down to a 6-2 7-5 defeat to France's Alize Cornet.
Third seed Garbine Muguruza of Spain advanced to the third round after her opponent, 16-year-old American Amanda Anisimova, withdrew due to a foot injury.
Katie Boulter exited at the first hurdle in her maiden premier event appearance after suffering a 6-4 7-5 defeat to Taipei's Hsieh Su-wei.
The 21-year-old beat Canada's Carol Zhao in qualifying to move into the first round proper but could not handle the experience and drop shot of Hsieh.
Hsieh won both sets with a delicate drop shot, the first set perhaps fortuitously via a net cord.
However, reaching the first round will see Boulter climb into the top 200 next week.