Jonas Gutierrez put the Magpies ahead in the first half before Chelsea surged into the lead courtesy of goals from Frank Lampard and Juan Mata.
However, Sissoko, who completed a move from Toulouse last Monday, scored from close range in the 68th minute before netting the winner on the stroke of full-time.
The 23-year-old signed a six-and-a-half-year deal at the Magpies, and Pardew was delighted to see the midfielder have an instant impact for his new club.
“He has fantastic power but, with players, you never know about their attitude until you get them in and start working with them,” said Pardew.
“But he came in like a giant and played like a giant. I remember watching him for Toulouse 14 months ago and thought, ‘he is the one for us’.
“We have watched him for a long time but we decided to accelerate it because he was going to come in the summer.
“But, my word, he is already paying us back handsomely.”
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