Defending champion David Ferrer suffered a shock straight-sets defeat to world number 147 Casper Ruud at the Swedish Open on Thursday.
The three-time winner was seeded seventh for this year's tournament but was beaten 7-5 6-2 by the Norwegian wildcard.
Ruud's reward is a clash with Richard Gasquet, who came from behind to reach the quarter-finals in a 1-6 6-3 6-1 victory over Gerald Melzer on the clay courts.
There were also wins for Fabio Fognini and Federico Delbonis on Thursday, with the pair now set to meet in the last eight.
Like Gasquet, Fognini recovered from a first-set drubbing to emerge with a 1-6 6-4 6-2 win against Mikael Ymer, while Delbonis accounted for John Milan 6-4 6-4.
At the Croatia Open Umag, fourth seed Andrey Rublev outlasted wildcard Felix Auger-Aliassime 6-4 6-7 (4-7) 6-3 and sixth seed Robin Haase overcame Martin Klizan 3-6 6-4 6-3.
However, second seed Damir Dzumhur crashed out following a 7-6 (11-9) 3-6 6-4 defeat to Evgeny Donskoy, while Marco Trungelliti rallied past Marton Fucsovics 5-7 6-4 6-2.
Meanwhile, at the Hall of Fame Tennis Championships, Ramkumar Ramanathan and Tim Smyczek progressed to a quarter-final against each other by beating Vasek Pospisil and Jason Jung respectively.