The Serbian initially struggled to settle as Nieminen broke his opponent at the first time of asking to take a 2-0 lead in the opening set, but his advantage was short-lived as Djokovic found his rhythm.
The top seed used his trademark athleticism and precision to break back instantly and push on to take a one-set lead in Monte Carlo.
Nieminen was required to launch a comeback in the second set, but Djokovic took full control of the clay surface by snatching a double-break to take a 3-0 lead, leaving Nieminen with plenty to do.
The Finnish pro was able to give himself a shred of hope by securing two games on the break, but Djokovic had just enough to move on and wrap up the contest.
The Serbian will face Fabio Fognini in the semi-finals.