Javier Pastore's 90th-minute goal at the Parc des Princes gave PSG a healthy cushion ahead of Tuesday's return game in London and Maxwell is confident they can finish the job and reach the semi-finals.
However, he is not getting carried away and says PSG must repeat their first-leg performance against a dangerous Chelsea side.
"It was a huge result. The game was very difficult, physically tough but we did a great job," said the Brazilian in the Daily Star Sunday.
"At 2-1 it was already a great scoreline When you beat a club like Chelsea it's always fantastic. But the late goal, for 3-1, makes it so much better.
"However, for us it's two feet firmly on the ground because we know how hard and tough it will be in London.
"Yes, we are very happy but we must go and do it again on Tuesday if we are to progress to the semis."
Chelsea have been criticised for the way they played in Paris but Maxwell believes they are side full of quality.
He said: "It's not for me to judge them. They have experience at the back and the up front, young, quick technical players."