Naomi Osaka lost her first match since moving up to No. 1 in the WTA rankings — and first since splitting from her coach.

The two-time major champion had trouble with her serve and was beaten 6-3, 6-3 by Kristina Mladenovic at the Dubai Championships in a little more than an hour on Tuesday.

Osaka had not competed since winning the Australian Open in January for her second consecutive Grand Slam title.

That victory also allowed her to become the first tennis player from Asia to lead the rankings.

Last week, Osaka announced on Twitter that she would no longer work with coach Sascha Bajin.

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Kristina Mladenovic, of France, returns the ball to Naomi Osaka, of Japan, during a match of the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Kristina Mladenovic, of France, returns the ball to Naomi Osaka, of Japan, during a match of the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Masashi Yoshikawa, Japan Tennis Association coach, shouts as he watches the match between Japan's Naomi Osaka and Kristina Mladenovic, of France, during the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Masashi Yoshikawa, Japan Tennis Association coach, shouts as he watches the match between Japan’s Naomi Osaka and Kristina Mladenovic, of France, during the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Naomi Osaka, of Japan, reacts during her match against Kristina Mladenovic, of France, at the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Naomi Osaka, of Japan, reacts during her match against Kristina Mladenovic, of France, at the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Naomi Osaka, of Japan, reacts during her match against Kristina Mladenovic, of France, at the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Naomi Osaka, of Japan, reacts during her match against Kristina Mladenovic, of France, at the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Kristina Mladenovic, of France, serves to Naomi Osaka, of Japan,  during a match of the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)
Kristina Mladenovic, of France, serves to Naomi Osaka, of Japan, during a match of the Dubai Duty Free Tennis Championship in Dubai, United Arab Emirates, Tuesday, Feb. (AP Photo/Kamran Jebreili)