Johnson's early onslaught saw the Stars slump to 4-26, forcing Seb Gotch (48 off 47 balls) and David Hussey (26 off 20) to launch a rescue mission.
But the Stars' total wasn't nearly enough in the high-stakes clash.
Johnson struck gold with the first ball of the innings when Rob Quiney was caught at fine leg for a golden duck.
Then three balls later, Luke Wright was also gone for nought when Ashton Turner took a sharp catch at gully, leaving the Stars at 2-0.
Johnson heaped more pressure on the Stars with a series of dot balls.
And a frustrated Pietersen eventually cracked, popping an easy catch to mid-wicket.
The first run Johnson conceded didn't come until the final ball of his third over.
And by the time Johnson finished his four-over spell, Melbourne were in all sorts of strife at 4-28.
Johnson's return of 3-3 was the equal third most economical figures in world T20 cricket, with only Chris Morris (2-2) and Chanaka Welegedara (4-2) conceding less runs over four overs.
Johnson received a standing ovation from the sellout crowd upon the completion of his fourth over.
The Stars needed quick wickets if they were to have any chance of winning.
The Scorchers should have been 2-27 when Whiteman edged a catch to the wicketkeeper.
But he was given not out by the umpire, much to the displeasure of Pietersen, who labelled the decision an absolute shocker.
Whiteman later hinted he had in fact edged the ball.
"There definitely was a sound," Whiteman said with a smile."
"We're not all like Gilly (Adam Gilchrist)".
It was the fourth time in five semi-final meetings the Scorchers have beaten the Stars.
"The first one I had in my mind I was going to knock his off pole out with a swinger, and it didn't quite swing back," Johnson said of Quiney's wicket.
"And off the bat I thought it was going for six, but nice catch down there for Jhye Richardson.
"It was nice to have luck go my way with that first ball. And to get another wicket in the over, it just set the tone.
"Stars captain David Hussey was disappointed with the loss."Of course it's frustrating. You want to win every game you play," Hussey said.
"I think a few of the boys are hurting tonight."But the fabric of the Stars, we're pretty strong and resilient, and we'll come back bigger and better next year."
MOST ECONOMICAL T20 BOWLING FIGURES OVER FOUR OVERS
4-2 Chanaka Welegedara
2-2 Chris Morris
3-3 Mitchell Johnson
1-3 Shoaib Malik
0-3 Sunil Narine
2-3 Zulfiqar Babar