Anna Blinkova overcame a fatigued Coco Gauff as the American teenager was unable to back up her Linz triumph at the Luxembourg Open.
Gauff claimed the first WTA title of her fledgling career in Austria last week but was clinically dispatched by Russian Blinkova 6-4 6-0 on Wednesday.
The beaten 15-year-old American complained of feeling tired as she was swept aside in the second set and found Blinkova in uncompromising mood.
World number 66 Blinkova made only five unforced errors and hit 18 winners in her first-round victory.
Defending champion Julia Goerges saw off 2015 winner Misaki Doi in a gruelling three-set battle, the second seed coming back to triumph 5-7 6-1 6-3 to reach round two.
Wednesday brought a more straightforward outing for third seed Elena Rybakina, who breezed past Denisa Allertova 6-2 6-1 to earn a quarter-final place.
Jelena Ostapenko beat Caty McNally in straight sets and will meet top seed Elise Mertens in the last-16, while there were second-round wins for Margarita Gasparyan and Laura Siegemund.
At the Kremlin Cup in Moscow, Belinda Bencic pulled off a stunning comeback to beat Polona Hercog 1-6 6-3 6-4 and book a quarter-final place.
As well as being blown away in the opening set, number three seed Bencic found herself 3-0 down in the decider before shifting through the gears to win six of the last seven games.
Bencic will next tackle Kirsten Flipkens, who bested fifth seed Dayana Yastremska 6-3 3-6 6-3.
Ekaterina Alexandrova had too much for fellow Russian Anna Kalinskaya, thrashing her compatriot 6-1 6-1 before their home crowd. Karolina Muchova, who stormed past fourth seed Donna Vekic 6-4 6-2, will be Alexandrova's last-eight opponent.