Caroline Wozniacki's Luxembourg Open campaign got off to a sticky start as she struggled past local girl Mandy Minella.
Top-seeded Wozniacki won the opening set 6-3 but was taken to a tie-break by the world no 114 in the second before winning it 7-2 to book her passage through to the second round.
It was much more straightforward for second seed Sloane Stephens who eased past Swiss wildcard Timea Bacsinszky 6-3, 6-3.
"It was tough," said the American. "Obviously playing a player I had never played before, or even seen play, was a little bit tricky.
"But I thought I played pretty good overall, so I was happy to get the win."
Next up for Stephens is Yvonne Meusburger, who defeated Irina-Camelia Begu 6-4, 6-2.
Sabine Lisicki of Germany suffered a scare but recovered to ensure that the top three seeds all made it through.
The German started slowly against Croatia's Donna Vekic and lost the opening set 6-2. But she dropped just three games after that to wrap up a 2-6, 6-3, 6-0 victory.
Two seeds did crash out though.
Fourth seed Kirsten Flipkens of Belgium lost to Katarzyna Piter of Poland 6-4, 6-2 while Germany's Mona Barthel fell to to Stefanie Voegele of Switzerland 1-6, 6-4, 7-6 (7-3).