Rotterdam, The Netherlands (SportsNetwork.com) - Top seed and defending champion Juan Martin del Potro came up a quarterfinal loser Friday at the $1.85 million ABN AMRO World Tennis Tournament.

Capable Latvian Ernests Gulbis took down the tall Argentine star, 6-3, 6-4, on the indoor hardcourts at Ahoy Rotterdam. Del Potro, who took a medical timeout after the first set, is on the mend from a wrist injury.

"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."

The former U.S. Open champion del Potro beat Frenchman Julien Benneteau in last year's finale and was the Rotterdam runner-up in 2012.

Also on Day 5, third-seeded Tomas Berdych came from behind to beat 6-foot-8 Pole Jerzy Janowicz, 6-7 (9-11), 6-2, 6-4, and secure a berth in Saturday's semifinals.