Defending champion Svetlana Kuznetsova suffered a humiliating first-round loss at the US Open on Monday.
The Russian has been struggling for form this year and came into the tournament with a back injury.
And the fifth seed made 45 unforced errors as she went down 6-3 6-2 to compatriot and world number 97 Ekaterina Bychkova.
Kuznetsova becomes the first defending women's champion to lose in the first round of the US Open.
Bychkova, making her first appearance in the main draw of a Grand Slam, broke three times on her way to winning the first set.
The 20-year-old then broke in the first and third games of the second to lead 3-0 before Kuznetsova gave herself a glimmer of hope by getting one of the breaks back.
But Bychkova broke again in the next game and clinched victory on her second match point after 65 minutes.
"I just didn't play my game," said Kuznetsova.
"I wanted it badly, it wasn't my day. Things weren't going my way."
She added: "I just do my best. You just cannot do anything more. I've been there, I tried, it wasn't my day.
"What do I do? Kill myself? I just take positive things out of this and maybe I'll learn."