Argentine qualifier Federico Delbonis upset eighth seed David Ferrer in the second round of the German Tennis Championships.
Ferrer captured his 27th tour-level title at last week's Swedish Open, but he was not able to overcome a spirited performance from Delbonis on the day.
The qualifier, who also reached the final here back in 2013, was a surprise 7-5, 6-3 winner on Thursday, earning him a quarter-final appearance against third seed Karen Khachanov.
The Russian World No 32 battled past Aljaz Bedene 7-6 (7-4), 5-7, 6-4 in two hours and 27 minutes.
Elsewhere, Local hope Phillip Kohlschreiber thrilled the fans with a 6-3, 3-6, 6-2 victory over fourth seed Gilles Simon.
There were also wins for Leonardo Mayer, Jiri Vesely and Nicolas Kicker.