The Serb praised veteran Nieminen, who is set to retire later this year, for coming out all guns blazing and taking a 3-1 lead in the first set. But, that was to be Nieminen's only high point of the match as Djokovic bounced back and dominated from there on in.
Djokovic is now just three wins shy of 650 tour-level victories and also saw his 2015 record improve to 43-3.
"I would rate [the match] probably around 7 or 8 [out of 10]," Djokovic told reporters. "I think it was a very solid performance. I've done just enough to win in straight sets. He started off very well, very aggressive, [with] winners in the first couple games. I managed to stay calm and believed that I could come back.
"That's what I've done. I think the crucial turning point was the 10th game of the first set when I won the set and I started playing more freely. I thought I had the match under control and everything was fine."
The defending champion will face 27th seed Bernard Tomic in the third round after the Australian beat Pierre-Hugues Herbert 7-6 (3), 6-4, 7-6 (5).
Despite having a 3-0 head to head advantage over Tomic, Djokovic knows that underestimating the Australian will be a grave mistake.
"I do expect him to serve well, and I do expect him to mix up the game [and] come up with a lot of variety," Djokovic said. "That's what he does. He's got a lot of talent in his hands. This is the surface that he loves playing the most on. So it's going to be a difficult match."