Frenchmen Richard Gasquet and Florent Serra and fifth-seeded Marcos Baghdatis of Cyprus also advanced to the second round while Sergiy Stakhovsky of Ukraine reached the quarterfinals.
Baghdatis beat Laurent Recouderc of France 6-4, 7-5, Serra edged Illya Marchenko of Ukraine 7-5, 7-6 (4), Gasquet routed Lukas Lacko of Slovakia 6-3, 6-0, and Stakhovsky defeated Andreas Seppi of Italy 7-5, 6-3.
Dolgopolov hit 11 aces and broke three times against Montanes, who beat Roger Federer in the Estoril Open semifinals en route to winning the title this month in Portugal.
The Ukrainian will next face Gasquet, a former top 10 player, who is looking to get back to his best after his career was hit by a suspension last year for testing positive for cocaine.
Gasquet took a 3-0 lead in the first set and concluded the match with a winning approach shot.
Baghdatis was initially scheduled to play Mario Ancic, but the Croat withdrew because of a back injury and was replaced by
Recouderc.
The Cypriot dropped serve only once and will next play Simon Greul of Germany.
Serra won the last five points of his first-round match after a double-fault gave Marchenko a 3-1 lead in the tiebreaker.
The Frenchman will meet second-seeded Fernando Verdasco of Spain.
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