Top seed Fabio Fognini reached the last eight at the ATP 250 clay-court event with a 7-6 (7-4) 6-2 triumph over Dustin Brown, while Tommy Haas and Andreas Seppi also prevailed in straight sets.
Fognini looked to be cruising as he won the opening three games against Brown, but the German fought back before losing the first set on a tie-break.
The second set was much easier for the world number 15 as he broke three times on his way to victory.
Fognini's fellow Italian Seppi took just under an hour and a half to see off Spain's Albert Ramos.
The seventh seed converted six of his 11 break-point opportunities and converted his second match-point to secure a 6-3 6-4 triumph.
Seppi will now face defending champion and second seed Haas, who eased past Alejandro Falla on his return to action.
Haas won four consecutive games in the opening set and completed his 6-2 6-4 win in 75 minutes.
The 36-year-old had been troubled by a shoulder injury in recent weeks and said: "I'm pretty happy with the win, obviously having been laid off for a couple of weeks and not knowing how the injury would be."
Lucky loser Ricardas Berankis, who replaced Gael Monfils in the draw, returned to court on Thursday to beat Jurgen Melzer 7-6 (7-5) 3-6 7-6 (8-6), having seen their second-round match suspended on Wednesday due to bad light.
Melzer had two match-points in the decisive tie-break, but was punished for his failure to take them.
Thomaz Bellucci is also through to the quarter-finals, the Brazilian coming from a set down to beat Federico Delbonis 5-7 6-3 6-2.