Djokovic dropped a tight first set before beginning to solve the game of Florent Serra and getting a 5-7, 7-5, 6-1 win. By the third set Djokovic had worn Serra down, was able to pile up three service breaks and advance to the grass-court tournament's quarterfinals.
Djokovic is to go against seventh-seeded Jurgen Melzer in Friday's quarterfinals, Melzer took the first set Thursday 6-1 when Nicolas Kiefer retired due to an abdominal muscle tear. Melzer and Djokovic are the only seeded players remaining in the Gerry Weber field.
Beck will meet Philipp Kohlschreiber while Tommy Haas goes against Mischa Zverev and Benjamin Becker plays Rochus in the quarterfinal round.
Beck, Becker, Haas, Kohlschreiber and Zverev are all from the tournament's host country of Germany.