Juventus got off to a flying start when Alessando Matri fired the Italian champions in front after just three minutes.
The Bianconeri then soaked up a lot of Celtic pressure before hitting them with two late goals from Marchisio and Mirko Vucinic.
Despite taking a three-goal lead back to Turin for the second leg on March 6, Marchisio is refusing to consider that the tie is over.
"It is a very important victory, especially as we can be a little more concentrated on Serie A," said Marchisio.
"We haven't passed through yet, but it is a great win in a difficult arena and we put in a fine performance.
"It's true it is tough to overturn a 3-0 away win, but we must never be certain and always go out there with the same determination.
"This team is having a great Champions League. This was an important signal to ourselves and nobody else. It was crucial to come here and score a goal, but we ended up getting three."
Juventus displayed some strong-arm tactics when defending corners with several players grabbling with each other and Marchisio admitted it was a planned move employed by them to keep Celtic at bay from set-pieces.
"We saw they scored many goals from corners and with crosses into the box, so tried our best to make it difficult for them," added Marchisio.
"It is their nature to be gritty and physical, but we gave as good as we got."