Top seeds Petra Kvitova and Caroline Wozniacki had to come from behind to beat Varvara Lepchenko and Sabine Lisicki respectively and advance to the Luxembourg Open quarter-finals.
Kvitova started off poorly by dropping her serve, and despite hitting straight back she was unable to stop Lepchenko moving into a one-set lead.
However, it kick-started a powerful recovery from the Czech who forced a decider as part of a run that saw her win nine successive games.
That streak included two breaks in the third which proved to be enough to secure a 4-6 6-2 6-0 scoreline set up a quarter-final meeting against Johanna Larsson, the Swede beating Mona Barthel 6-1 6-4.
Second seed Wozniacki, who has been struggling with illness this week, also had to fight from one set down to win her match against Lisicki 3-6 6-2 6-3.
The Dane was in danger of letting a 4-1 lead in the decider slip when she suffered a break in game seven, but she won the next two to reach the last-eight.
Monica Niculescu awaits following her 3-6 7-5 6-4 win over wildcard Francesca Schiavone.
The other quarter-finals pit third seed Kiki Bertens, who beat Anna Karolina Schmiedlova in straight sets, against Denisa Allertova and qualifier Lauren Davis with Andrea Petkovic.
Petkovic booked her place by comfortably dispatching of fourth seed Caroline Garcia 6-1 6-1.