Serena and Venus Williams each saw their run at the ASB Classic come to an end on Wednesday.
Venus had to withdraw due to an arm injury after playing the first of her two scheduled matches for the day, but Serena was stunned in windy conditions by fellow American Madison Brengle.
Serena had raced into a 4-1 lead in the first set, but clunky footwork in blustery weather cost her as Brengle won five successive games to seize the initiative.
The secret to Brengle's success? Playing terribly, she claimed.
She asked coach Nicole Melichar at one changeover: "I feel like if I play even uglier off the return is that a good idea?