Jelena Ostapenko, Venus Williams and Coco Vandeweghe were the biggest names to crash out on day one of the Madrid Open on Saturday.
Eighth seed Williams fell at the hands of Anett Kontaveit, losing 3-6 6-3 6-2 in a miserable start to her clay-court season.
Stuttgart Open finalist Vandeweghe was less convincing in a 7-5 6-0 defeat to Kristina Mladenovic, who also beat the American in the Fed Cup last month, and another big result saw fifth seed Ostapenko lose 6-3 6-3 to Romanian Irina-Camelia Begu.
Elsewhere, there were victories for Elina Svitolina, Karolina Pliskova and Caroline Garcia.
Simona Halep, Caroline Wozniacki, Garbine Muguruza and Maria Sharapova are among the stars who will begin their campaigns on Sunday.
It was Ostapenko's first career match against Begu, but not one she will remember fondly.
The world number five struggled in the opening set, forcing only two break opportunities as Begu consistently won vital points on second serve, while breaking her opponent in the first and last games to move in front.
Ostapenko offered more resistance in a second set that saw five consecutive breaks of serve, before Begu held to love in the ninth game, her victory sealed when the 2017 French Open winner sent a tired backhand into the net.
WILLIAMS WOBBLES AS VANDEWEGHE FALLS TO FAMILIAR FOE
Kontaveit impressed by reaching the semi-finals in Stuttgart last week and produced an impressive comeback to see off the veteran Williams.
The Estonian was aggressive throughout, registering 42 winners as well as 42 unforced errors, and she claimed victory with her second match point when her 37-year-old opponent sent a backhand long.
"Every match in Stuttgart gave me a little bit of confidence, and now I'm feeling really good on clay, like I can beat anyone," Kontaveit said to WTA Insider.
Vandeweghe fell at the first hurdle to Mladenovic, shortly after being beaten by the world number 22 in the Fed Cup on the same surface.
In a match where poor serving was on display, there were five breaks in a topsy-turvy first set that Mladenovic edged, before she raced clear to seal the win in the second.
SVITOLINA AMONG SEEDS TO EASE THROUGH
Svitolina was the highest seed in action on Saturday and she got her campaign off to a routine start with a 6-2 6-2 victory over Alize Cornet.
The fourth seed has never made it past the second round in Madrid, but she will have the chance to improve on that record after hitting 28 winners to wrap up a fourth consecutive victory against Cornet in only 71 minutes.
Garcia was tested slightly more but also progressed in relative comfort with a 6-1 7-5 triumph over Dominika Cibulkova, who was a finalist in this tournament two years ago.
There were also no problems for Julia Goerges, Pliskova and Daria Kasatkina, who all won in straight sets against Timea Babos, Elena Vesnina and Qiang Wang respectively.
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