Top-seed Flavia Pennetta has been knocked out in the first round of the Tianjin Open by a player 406 places below her in the world rankings.
Ukranian qualifier Lyudmyla Kichenok, the world number 414, took just over an hour and a half to beat the US Open champion 6-3 7-5.
In both sets Kichenok broke first before Pennetta hit back, but the Italian then gave up her serve again to go down in China.
It is the second week in a row she has exited a tournament early after losing in the China Open third round.
Kichenok will face qualifier Ying-Ying Duan in the second round.
