Del Potro had a bye as the event's No. 1 seed and so Thursday marked his first appearance. It was relatively short as he dispatched Rui Machado 6-1, 6-0 in 62 minutes.
He finished off 5-of-6 break-point chances and won 72 percent of the points on serve and 70 percent overall for the match.
Del Potro next faces seventh-seeded Albert Montanes in the quarterfinals. Montanes shook off a challenge from Bobby Reynolds for a 6-4, 4-6, 6-3 win Thursday. There were only four breaks in 29 games, but three were by Montanes.
The other quarterfinal set Thursday has fourth-seeded Albert Ramos playing wild-card entrant and local favorite Joao Sousa. Ramos beat Bjorn Phau 7-5, 6-0, losing only 13 points in the second set. Sousa advanced when fifth-seeded Denis Istomin retired after Sousa was up 3-6, 6-3, 4-2.