The Australian top seed, has recently been struggling to rediscover last year's form, which saw him rise to No 2 in the world rankings. But in the Netherlands he picked up his fourth career title with a 7-6, 6- 2 victory.
Rafter, now ranked No 6, said he needed the win to build up some self- esteem before Wimbledon and added, "If I were a betting man, I would put money on Pete [Sampras]. He is still awesome."
In searing heat, both players held their serve in the first set, but Damm seemed to lose his concentration at the start of the tie-break when the umpire called wide a smash which appeared to hit the line.
Rafter, who won last year's US Open, went on to win the tie-break 7- 2.
Damm, ranked 85 in the world, failed to recover from the ruling, and then managed to drop his opening service game of the second set to give Rafter the advantage. The Australian broke Damm again in the seventh game to seal the match.
Damm, who hurt his right shoulder during the French Open, said the injury was again troubling him. "But I don't want to blame my loss on the injury, I lost to a great guy on grass," Damm said.