Second seed Stefanos Tsitsipas suffered a surprise 7-5 6-4 defeat to unseeded Slovenian Aljaz Bedene in the last 16 of the Rotterdam Open on Thursday.
Tsitsipas had five break points in the first set but failed to convert any and Bedene fought back to take the set.
World number 52 Bedene then broke Tsitsipas at 1-1 in the second set before serving out to secure the win.
He will play Canadian teenager Felix Auger-Aliassime in the quarter-finals.
"To win against a top 10 player feels great," Bedene said. "It's only my second time.
"I am serving really well lately. I'm trying to stay focused on my serve, especially against big players with big serves where you don't get many chances. I guess I served well in the important points and kept my cool."
Tsitsipas's exit follows that of top seed Daniil Medvedev, who was beaten by Vasek Pospisil 6-4 6-3 on Wednesday.