In a re-match of last year's final, the American top seed struggled to find his game but eventually lined up a meeting with Thomas Johansson, another two-time Stockholm champion.
The Swede delighted the home crowd with a 4-6 7-5 7-6 victory over Croatia's Mario Ancic.
"I don't know what it is about Stockholm, but it brings out the best in me," said Blake.
"Right now I am tired, but happy. And I know Thomas had very tough match just like me."
With superb counter-punching and his deft touch, Nieminen came back from 5-2 in the first set to eventually outplay the American in a tiebreak 7-1.
Had Nieminen taken some of his chances in the following set, he would have won as Blake fought off break points in three of his service games, most notably when he was down 2-1 and 0-40.
But Blake pulled off some gutsy offensive play in the decisive moments to stay in the match and broke Nieminen to reach 6-4 and a third set.
Having found his groove, Blake went on to break Nieminen in the first and third gamed of the decider to wrap up the win.
Johansson, the 2000 and 2004 champion, was made to fight all the way in a match lasting two hours and 21 minutes.
HIGH PACE
"I am going to have to play at a very high pace against James," said Johansson, who won his only match of three meetings with the American last month in Sweden's Davis Cup loss to the United States in Gothenburg.
"I will have to stay aggressive and attack his serve all the time and stop him from pushing me around the court the way he can."
Earlier, fourth seed Tommy Haas set up a semi-final clash with Ivo Karlovic, another Croatian, by beating Juan Monaco 6-3 6-3 in his first match against the Argentine.
German Haas, a former world number two, grabbed a 5-0 lead in the opening set before Monaco found some momentum in his serve and broke back once before the German served it out.
In the second the Argentine never threatened Haas, who will contest the second Stockholm Open semi-final of his career. In 2004, he was narrowly beaten by Andre Agassi in the last four.
Haas, who won his 11th ATP title in Memphis this year, has lost three of his four meetings with giant server Karlovic, who blasted 30 aces past Frenchman Arnaud Clement in his match to win 7-6 3-6 7-6.
Karlovic, the seventh seed who is chasing his third title of the year, needed two hours and 23 minutes to take his third win in six meetings with Clement, the former world number 10 and 2001 Australian Open finalist.
The Croatian accomplished the rare feat of beating an opponent without breaking serve, saving a match point in the decisive tie-breaker before wrapping it up 9-7 with an ace.
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