The fourth-seeded Ljubicic never faced a break point and sealed the win with his 18th ace. He won every point on his serve in the tiebreaker.
"I feel great. Today was good, I was able to play aggressive the way I wanted and everything went pretty good," Ljubicic said, admitting that he felt tired heading into the match. "That's why I kept the points very short, I went for winners. I made a lot of mistakes but I knew that I couldn't play with him left and right, 10 shots."
Monfils won an all-French semifinal against Davis Cup teammate Jo-Wilfried Tsonga 7-6 (2), 2-6, 6-4. It was Monfils' first win over the second-seeded Tsonga in three matches on the main tour.
Ljubicic won last year when the tournament was held in Lyon and in 2001 for his first career title.
"I have a fantastic record in France. I have won three titles here, played the final in Bercy, semifinal in Roland Garros and now here," said Ljubicic, who also won an indoor title in Metz five years ago.
Ljubicic is looking for his 11th career title and second of the year. The Croat beat top-ranked Rafael Nadal and No. 3 Novak Djokovic on his way to his first Masters title at the BNP Paribas Open at Indian Wells in March.
Monfils save one break point in the first game against Tsonga, and they then stayed on serve till the tiebreak. Monfils raced to a 5-0 lead and set up a set point with a drop shot followed by a volley and clinched it with his fourth ace.
He then wasted three break points in the second set and lost his serve twice as Tsonga recovered with a consistent first serve.
But Monfils lost only six points on his serve in the decider and converted one of his two break chances to reach his third final this year.