Naomi Osaka of Japan was beaten in her debut match as world number one by Kristina Mladenovic in the second round of the Dubai Duty Free Tennis Championships on Tuesday.
It was also the Japanese’s first match since her split from coach, Sascha Bajin.
Having received a first-round bye at the event, Osaka kick-started her campaign in the second round against Mladenovic who, before this week, had not won a singles match in 2019. But the Frenchwoman would turn the tables, breaking the Australian Open champion seven times to clinch a 6-3, 6-3 victory in just over an hour and advance to the third round.
She will next play Carla Suarez Navarro for a place in the quarterfinals.
Elsewhere, Wimbledon champion Angelique Kerber rallied from being 5-1 down in the first set to Dalila Jakupovic to win 7-6, 6-3 and advance to the third round.
Meanwhile, world number two, Simona Halep fended off a spirited challenge from Eugenie Bouchard to prevail 7-6, 6-4 and set up a third round match with Lesia Tsurenko on Wednesday.
This year’s Australian Open finalist, Petra Kvitova overcame a slow start to book her place in the last 16. The world No.3 had looked out of sort against Czech compatriot Katerina Siniakova before regaining composure to claim a 6-7, 6-4, 6-4 victory in two hours and 35 minutes of absorbing tennis.