Luxembourg - Top-seeded Caroline Wozniacki beat two-time finalist Monica Niculescu of Romania 6-3, 6-2 to reach the quarter-finals of the Luxembourg Open on Thursday.
Wozniacki joined second-seeded Sloane Stephens of the United States, who advanced by beating Yvonne Meusburger of Austria 7-5, 6-4.
Sabine Lisicki made it a perfect day for the top three seeds when the German defeated Tereza Smitkova of the Czech Republic 6-4, 6-0.
Stephens, ranked 12th in the world, has yet to lose a set in Luxembourg and will play Stefanie Voegele on Friday. The 54th-ranked Swiss player struggled to beat Karolina Pliskova of the Czech Republic 6-1, 3-6, 6-3.
In another second-round match, Karin Knapp of Italy beat Andrea Petkovic of Germany 7-5, 7-5.