Clijsters, No. 2 in the world and seeded first at 's-Hertogenbosch, edged Monica Niculescu 7-5, 7-5. She finished the victory on her fifth match-point opportunity.
There were 10 service breaks over the 24 games with Clijsters needing four to claim the first set and getting two more in the second.
No. 2-seeded Svetlana Kuznetsova and third-seeded Yanina Wickmayer had easier times of it in their first-round matches. Kuznetsova ousted Arantxa Rus 6-2, 6-4 behind five service breaks and Wickmayer won 61 percent of the points in a 6-4, 6-0 decision over Alberta Brianti.
Fourth-seeded Flavia Pennetta got past Alona Bondarenko 6-4, 6-4 but Kimiko Date-Krumm upset No. 6-seeded Maria Kirilenko 7-6 (7-5), 6-2.
Qualifier Romina Oprandi defeated Akgul Amanmuradova 6-4, 6-3 and Alexandra Dulgheru slipped past Alison Van Uytvanck 7-5, 7-6 (9-7).
Arantxa Parra Santonja beat Laura Robson 7-5, 6-3 and Kristina Barrois swept by Barbora Zahlavova Strycova 6-3, 6-2.