The Japanese star had enjoyed a bye through the first round of competition at the Women's Tennis Association Premier 5 event at the Aviation Club Tennis Centre in Dubai.

Osaka faced the challenge of Kristina Mladenovic in her first match as world number one, following her second straight Grand Slam triumph at the Australian Open.

The French player sprung a surprise as she broke Osaka's serve on seven occasions to eventually emerge as a straight sets 6-3, 6-3 winner.

The result was a blow for Osaka, who opted to split from her coach Sascha Bajin prior to the tournament.

Mladenovic’s reward is a third round meeting with Spain’s Carla Suarez Navarro, who beat China’s Zhang Shaui 6-4, 6-4.

Romania’s Simona Halep, who was displaced by Osaka as world number one, won her opening match of the tournament.

She claimed the opening set on a tie-break against Canada’s Eugenie Bouchard, before sealing a 7-6, 6-4 win against the wildcard.

Halep will now face the challenge of Ukraine’s Lesia Tsurenko, who edged China’s Zhu Lin 6-4, 6-7, 6-3 in their second round match.

Australian Open runner-up Petra Kvitova was forced to come from a set down in an all-Czech Republic match against Katerina Siniakova.

Kvitova recovered from losing a first set tie-break to ultimately win 6-7, 6-4, 6-4.

She will American qualifier Jennifer Brady for a place in the quarter-finals of the tournament.

Brady beat France’s Caroline Garcia 6-5, 7-5.