The left-hander survived two tiebreaks while rallying to a 4-6, 7-6 (2), 7-6 (8) victory to record his sixth career ATP title.
Making the victory sweeter for Lopez was the realization that he really did prevail at The Queen's Club.
"It's the best week of my career, I would say," Lopez told reporters following the match. "To win this tournament at this stage of my career, this is so amazing. I was waiting so long to win this title. Queen's is the best. Outside of the Grand Slams, this is one of the most special tournaments.
"You feel the atmosphere here, all over the years, a tradition that this tournament, the players that have won in the past. For me to be here on Sunday holding the trophy, it's the best feeling I can have."
In fact, some demons from 2014 emerged while Lopez was serving for the match. He was in the same position at The Queen's Club that year in the final against Dimitrov and lost the point and eventually lost the match.
"It was tough to put that match out of my mind," Lopez said. "I was serving for the match again. It was tough to handle my nerves."
This time Lopez got it done as Cilic's errant forehand in the third-set tiebreak ended the two-hour, 32-minute match.
Cilic delivered more aces (22 to 19) but lost the momentum he had in the opening set. Lopez took advantage to continue his recent stretch of stellar tennis.
"I am probably playing my best tennis," Lopez said. "It is hard to believe when you are 35 years old.
"I am so happy. This is the best preparation to go into Wimbledon next week. It is a great feeling."
Cilic was aiming for his second Queen's Club crown. He won the title in 2012.
"Looking at the whole week, it was great tennis for me," Cilic said. "I have to say maybe one of the best grass-court tournaments for me overall throughout my career, looking at the consistency of my game. I lost only once my serve during the whole week, which is amazing, considering last week I didn't lose serve in Netherlands, too. That makes it even better.
"Looking at my game, I'm feeling great on the court, moving well, playing well. I was even today against Feliciano making more pressure on him, on his service games than what he did on mine. That's another plus. So overall, I'm feeling really satisfied and I think I need just now a few days to recover mentally. Then I can continue with good form."
As for Lopez, being referred to as a Queen's Club championship seemed a bit surreal.
"I cannot believe I have finally won this tournament," Lopez said. "I have wanted to win this for 15 or 16 years."