Angelique Kerber was given a scare by Annika Beck before getting her Stuttgart Open defence off to a winning start on Wednesday.
The Australian Open champion struggled to live with her German compatriot in the opening set as Beck's powerful groundstrokes produced a string of winners.
She was unable to maintain that form, though, as Kerber found her rhythm, and despite 31 unforced errors in the match the second seed was able to record a 4-6 6-3 6-1 win.
Kerber is joined in the quarter-finals by Garbine Muguruza after the third seed brushed aside Timea Babos 6-2 6-2, the Spaniard far too good in all areas for her Hungarian opponent.
Eighth seed Lucie Safarova was a surprise casualty in the remaining first-round matches as she was beaten in three sets by Karolina Pliskova, who won 7-6 (7-4) 4-6 7-5.
There was little between the Fed Cup team-mates until Pliskova applied late pressure, the 24-year-old went on to convert her seventh match point to set up a clash with Ana Ivanovic.
Roberta Vinci was also pushed by Ekaterina Makarova in her opening match, the sixth seed eventually prevailing 7-6 (7-3) 4-6 6-4.
Julia Goerges, Andrea Petkovic and Monica Niculescu also enjoyed first-round wins, the latter setting up a meeting with Petra Kvitova in round two.