Del Potro collected the first of his five 2013 titles last year at the Rotterdam ATP stop and cooled off Monfils in his first match in the tournament this year with a 7-6 (8-6), 6-3 first-round decision. Monfils, coming off a tournament win Sunday in France, had won six straight matches before falling to del Potro.
Del Potro was able to cash in three of his four break chances for the win. He saved the only break point he saw in the second set while finishing off the only opportunity he had himself.
The second round began with an upset as Marin Cilic, like Monfils boasting a tournament title Sunday, topped No. 5-seeded Jo-Wilfried Tsonga 6-4, 6-4. Cilic won 79 percent of the points on serve, losing 11 points over 10 games serving.
The other matches Wednesday all in the first round.
No. 4-seeded Richard Gasquet battled for nearly 2 1/2 hours before claiming a 6-7 (5-7), 7-6 (7-2), 6-3 decision over Thiemo de Bakker and sixth-seeded Tommy Haas did need 2 1/2 hours to get past Fernando Verdasco 6-7 (4-7), 7-6 (7-1), 7-5.