Both remaining seeds in the German Tennis Championships were bundled out in the quarter-finals in Hamburg.
Karen Khachanov, the third seed, was beaten 7-5 3-6 6-4 by qualifier Federico Delbonis, ranked No.81.
Delbonis reached the final four years ago after beating Roger Federer in the last four and will face fellow Argentine Leonardo Mayer in the semi-finals.
Lucky loser Mayer, the 2014 champion whose ranking has slid to No.138, defeated Jiri Vesely 7-6 (7-4) 6-3.
Their compatriot Diego Schwartzman, seeded sixth, suffered a surprise loss to world No.101 Florian Mayer.
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The German won 6-2 3-6 6-3 to set up a showdown with compatriot and fellow 33-year-old Philipp Kohlschreiber.
The veteran edged Nicolas Kicker 7-6 (8-6) 4-6 6-4 in two hours and 37 minutes to reprise his 2014 appearance in the semi-finals.
