Top-seeded Grigor Dimitrov lost his opening match at the Grand Prix Hassan II, bowing out against veteran Tommy Robredo 6-4, 1-6, 6-1 on Thursday.
The 34-year-old Robredo, now ranked 385th, saved seven of nine break points and converted all three chances he got to win on Dimitrov's serve.
Robredo will face Benoit Paire in his first tour-level quarterfinal match since he reached the semifinals at Shenzhen Open in 2015. Paire beat Radu Albot 6-2, 6-2.
Fourth-seeded Mischa Zverev was also eliminated, losing to Jiri Vesely 6-4, 6-4, while fifth-seeded Paolo Lorenzi advanced by beating Gianluigi Quinzi 7-6 (5), 2-6, 6-4.