Brothers Jurgen and Gerald Melzer will meet in the quarter-finals of the Generali Open after the two leading seeds were knocked out in Kitzbuhel.
With Gerald having already made the last eight, Jurgen - ranked 421st - sprung a shock by beating top seed and world number nine Dominic Thiem 6-3 7-5.
Reigning champion Philipp Kohlschreiber, seeded second, was another surprise loser as he went down 6-4 6-4 to Karen Khachanov.
Elsewhere, there was a straight-sets win for top seed Feliciano Lopez, who beat Jan Mertl 7-6 (7-4) 6-4 in the pick of the day's results from the Swiss Open Gstaad.
Mertl had on Monday won his first main-draw match at the age of 34.
And at the Croatia Open in Umag, fourth seed Fabio Fognini overcame Argentina's Renzo Olivo, while eighth seed Jiri Vesely retired hurt in another last-16 match against Carlos Berlocq.