SHERTOGENBOSCH (Netherlands) (AFP) Top seed Justine Henin continued to flex her muscles on grass ahead of Wimbledon as she advanced to the semi-finals of the ATP-WTA tournament here on Thursday. Belgian Henin, champion at this event in 2001 but playing it for the first time since 2003, has not dropped a set so far in the grasscourt tournament and saw off Germanys Kristina Barrois 7-5, 6-3. The two-time Wimbledon runner-up next meets Romanias Alexandra Dulgheru. Fifth seed Dulgheru, playing just her second Tour event on grass, rallied from a set down against fourth seed Yaroslava Shvedova of Kazakhstan to win 3-6, 6-3, 6-4. Germanys Andrea Petkovic, the seventh seed, ended the run of Czech qualifier Sandra Zahlavova 6-2, 7-6 (7/5), and next meets Belgian Kirsten Flipkens, who eased past Slovak Dominika Cibulkova 6-2, 6-3. In the mens event, defending champion Benjamin Becker beat fellow German Simon Greul 6-3, 6-1 in their quarter-final tie. Becker, seeded eight, trailed 1-3 in the first set, but hit back to win five games in a row to take the set. The world number 48 then broke in the fourth and sixth games of the second set before serving out victory to love with his seventh ace. Becker is through to his second semi-final in a row after reaching the final four on grass in Halle, where he lost to eventual champion Lleyton Hewitt. He next plays seventh seed Janko Tipsarevic of Serbia, who came through 6-3, 6-3 against Australian Peter Luczak. Elsewhere, 71st-ranked Sergiy Stakhovsky reached his first ATP semi-final of the year by easing past Colombian Santiago Giraldo 6-3, 6-4. The 24-year-old Stakhovsky will next face Xavier Malisse after the Belgian, a quarter-finalist last week on grass at The Queens Club, saved nine of 12 break points to beat another Colombian, Alejandro Falla, 6-3, 3-6, 6-3.