Second-seeded Martin Klizan of Slovakia withstood a strong challenge from Germany's Dustin Brown to win 6-4, 4-6, 7-6 (5) and reach the quarterfinals of the Grand Prix Hassan II on Wednesday.
In an evenly-matched contest, both players had three aces and dropped serve four times each.
Klizan's quarterfinal opponent will be Spain's Nicolas Almagro, who did not concede a single break-point chance in a 7-5, 7-5 win against Argentina's Carlos Berlocq.
Sixth-seeded Andreas Haider-Maurer of Austria also advanced to the last eight after beating Spaniard Pablo Andujar 7-5, 6-3.
Haider-Maurer, who had nine aces and saved all four break-point chances on his serve, next plays Bosnian Damir Dzumhur, who was leading 3-0 against Marcel Granollers, when the fourth-seeded Spaniard retired.
Top-seeded Guillermo Garcia-Lopez is in second-round action on Thursday when he takes on Russian Mikhail Youzhny.