Shanghai - Reigning champion Aryna Sabalenka and top seed Belinda Bencic suffered shock defeats at the Shenzhen Open on Tuesday, dealing a setback to their Australian Open preparations.
World No 11 Sabalenka lost 6-4, 6-4 to the Czech left-hander Kristyna Pliskova as the Belarusian's title defence came to a juddering halt in the second round.
Earlier, on a day of upsets in southern China, world No 8 Bencic was defeated in her opening match of the year.
The Swiss was a surprise loser to the 58th-ranked Anna Blinkova, the Russian coming back from a set down to win 3-6, 6-3, 6-3.
"I didn't feel great in the beginning of the match," said Blinkova, 21, after claiming the biggest scalp of her career.
"I didn't feel the ball and my shots. I didn't play bad, but I managed to increase the level of my game slowly, step by step."
The Australian Open, the first Grand Slam of the season, begins in just under two weeks.