Australian Open semi-finalist Coco Vandeweghe was bundled out of the Dubai Tennis Championships by compatriot Alison Riske in the first round on Monday.
Vandeweghe defied the odds to put together her best run at a grand slam in Melbourne last month, but the 11th seed fell at the first hurdle in the United Arab Emirates.
Powerful world number 21 Vandeweghe has only played in the Fed Cup since her loss to Venus Williams at Rod Laver Arena and Riske took advantage of a below-par display from her America team-mate to win 6-4 6-4.
There were 11 double faults from Vandeweghe and Riske broke five times to wrap up a straight-sets victory.
Caroline Wozniacki moved into the second round with a 6-2 7-5 defeat of Daria Kasatkina two days after losing to Karolina Pliskova in the final of the Qatar Open.
The 10th seed from Denmark, who has risen to 15th in the rankings, failed to hold in the first game of the match but responded to set up a meeting with Viktorija Golubic.
Christina McHale and Catherine Bellis claimed the scalps of seeds Kiki Bertens and Yulia Putintseva respectively, while Olympic champion Monica Puig was among the other first-round winners on day two of the hard-court tournament.
There were no shocks in the Hungarian Ladies Open, but second seed Lucie Safarova needed a final-set tie-break to beat Magda Linette 6-0 5-7 7-6 (7-4),
Pauline Parmentier had to get herself out of trouble to see off Kateryna Kozlova 7-6 (7-3) 7-6 (7-2), while Annika Beck, Donna Vekic and Hsieh Su-wie also prevailed.