Top-seeded Juan Martin del Potro and number two Andy Murray both crashed out at the ABN Amro Friday, leaving Tomas Berdych as the only seeded player to reach the semifinals.
Ernests Gulbis of Latvia upset defending champion Del Potro 6-3, 6-4. The Argentine is recovering from a wrist injury and it wasn't clear whether it may have been bothering him. He took a medical time-out after the first set, but decided to continue.
However, his service appeared to suffer: in the first set, he served five aces to Gulbis' six. In the second, Gulbis had six more while Del Potro had none.
"It's nice to have beaten the defending champion, but actually it doesn't matter to me who won last year or 10 years ago," Gulbis said. "I'm through to the semifinals, and that's the most important."
Cilic beat Murray 6-3, 6-4 in an hour and 11 minutes, making it look easy in what was his second win over the Scottish Wimbledon champion in their 11 meetings. After Murray failed to hold serve in the fifth game of the second set, he had four chances to break back in the sixth - but failed to capitalize.
Third-seeded Czech 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 one semifinal.
In the other, Cilic will play the winner of Friday's final match, between hometown favorite Dutchman Igor Sijseling and Philipp Kohlschreiber of Germany.