Second seed Roberto Bautista Agut beat Marius Copil 4-6 7-6 (7/3) 7-5 to advance to the quarter-finals of the BMW Open in Munich.
He will next face German qualifier Yannick Hanfmann, who shocked eighth seed Thomaz Bellucci.
Hanfmann – at 273 in the world, ranked 216 places lower than his Brazilian opponent – triumphed 7-6 (7/5) 4-6 7-5 after saving match point in the final set.
There were no such problems for the third seed Alexander Zverev as he beat Jeremy Chardy 6-4 6-4 to set up an all-German meeting with Jan-Lennard Struff, the seventh seed who got past another home favourite, Tommy Haas, 6-4 7-5.
Meanwhile, at the Estoril Open in Portugal, top seed Pablo Carreno-Busta beat Tommy Robredo to progress to a last-eight match against Nicolas Almagro, the man he lost to in last year's final. Almagro booked his spot by defeating Gastao Elias.
There was also victory for second seed Richard Gasquet over Carlos Berlocq, with the Frenchman now set to face Kevin Anderson, who beat qualifier Joao Domingues.
