Ernests Gulbis of Latvia has upset top-seeded Juan Martin del Potro 6-3, 6-4 to book a place in the semifinals of the ABN Amro tournament.
Del Potro, who is also the tournament's defending champion, saved four break points in the first set. The Argentine is recovering from a wrist injury and it is not clear whether it may have been bothering him.
Earlier Friday, third-seeded Czech Tomas Berdych survived a difficult first set, including a tiebreak in which he had five set points. He regrouped and went on to win 6-7 (9), 6-2, 6-4 against Jerzy Janowicz of Poland. Berdych and Gulbis will meet in the semifinals.
Later Friday, second seed Andy Murray plays Marin Cilic, and hometown favorite Dutchman Igor Sijseling faces Philipp Kohlschreiber of Germany.