Top seed Roberta Vinci suffered a humiliating first-round defeat against rank outsider Chang Kai-chen at the Malaysian Open on Tuesday.
The world number 10 was expected to ease past Chang after entering as a wildcard, but fell at the first hurdle after suffering a shock 5-7 6-2 6-1 defeat in Kuala Lumpur.
Vinci, who became the oldest player in WTA history to enter the top 10 in the world rankings last month at the age of 33, was broken seven times and four breaks of her own were not enough to prevent an early exit at the hands of the world number 153.
Chang threatened to win the first set when she opened up a 3-1 advantage, but last year's US Open runner-up fought back to thwart the 25-year-old from Chinese Taipei.
Vinci won the St Petersburg Ladies Trophy last month, but there will be no second title of the year this week after Chang broke three times to level the match and twice in the decider to stun the experienced Italian.
Annika Beck, seeded eight, also bowed out with a 7-5 6-3 defeat at the hands of the 95th-ranked Zarina Dyas.
Dyas grasped half of her 10 break-point opportunities and failed to hold just once to seal her place in the second round.
There was also disappointment for eighth seed Zheng Saisai of China, who beat Australian Open champion Angelique Kerber before being knocked out in the quarter-finals of the Qatar Open last week, as she lost 4-6 6-3 6-2 to compatriot Yang Zhaoxuan.
Elina Svitolina, the second seed, saw off Miyu Kato in straight sets, while Risa Ozaki, Cagla Buyukakcay, Zhu Lin and Naomi Broady also advanced.