The 23-year-old Bulgarian fourth seed recovered from a set down and saved a match point in the second to register his fourth career title, all of them since last November.
Dimitrov, a former Wimbledon junior champion, is now the first player this year to win titles on three different surfaces after winning on the hard courts in Acapulco and the clay of Bucharest.
"It was amazing," Dimitrov said during the presentation of the trophy - one of the biggest in the sport.
"It's been amazing coming here every year and playing that tournament means a lot to me. I'm really happy to go through that match in such a way.
"There's some good matches ahead to Wimbledon and I'm excited for the time ahead.
"I knew it was not easy to break Fel. Especially in moments like that he's been serving so well all week. He's been tremendous all week. It was a great fight."
The first set was tense affair with neither player able to break serve on the way to a tiebreak.
Lopez looked to have gained the ascendancy leading 5-2 in the breaker but a series of unforced errors gifted Dimitrov a route back into the set.
The Spaniard had four set points but it wasn't until the fourth when the Bulgarian slipped and hit his attempted passing shot into the net to hand the 10th seed the first set.
Dimitrov was on the brink of defeat in the 10th game of the second set but he saved a match point and held his nerve to stay in the contest and force a deciding set with a dominant display in the second set, offered up only one point.
Again Dimitrov found himself up against it in the third set but his fighting spirit was evident as he recovered from a break down, although a double fault from Lopez helped.
Inevitably a third tiebreak was required to separate the two players and it was Dimitrov who edged it, leaving left-hander Lopez disconsolate.
"I was one point away from the victory," he said. "It's very disappointing but this is tennis and you have to accept it."
"It was a tough match to lose like this but it's definitely great preparation for Wimbledon.
"I played five or six matches this week. It's a beautiful place and there is no better preparation."
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