Croatian Borna Coric showcased his potential once more by ending Jeremy Chardy's Estoril Open campaign in straight sets.
At 18, Coric is the youngest player in the ATP's top 100 but needed just 83 minutes to see off Chardy 6-2 6-4 despite making four double faults.
Coric will face either Rui Machado or Joao Sousa in the second round while Robin Haase is to take on top seed Feliciano Lopez.
The Dutchman came through a hard-fought contest with Ricardas Berankis to win their first career meeting 6-3 6-7 (6-7) 6-4.
Haase slipped out of the world's top 100 following a first-round exit to Albert Ramos-Vinolas during the Monte Carlo Masters earlier this month.
And despite converting just five of 17 break-point opportunities, Haase hit the comeback trail as he proved too strong for the Lithuanian.
Eighth seed Gilles Muller was given a stern workout by Portuguese wildcard Frederico Ferreira Silva before winning through 6-3 3-6 6-1 in just short of two hours.
Having surged 3-0 ahead en route to taking the first set, Muller was given a tougher test in the second as Muller got the crucial break to level matters.
However, the 235-place gap in the world rankings told eventually as Muller wrapped up the victory in a brisk third set, joining Filip Krajinovic in the last 16, after his 6-3 6-3 win over Colombia's Alejandro Gonzalez set up a second-round clash with Ramos-Vinolas or Australian seventh seed Nick Kyrgios.