Pazzini volleyed home in the 21st minute to put Inter, who are 17th in Serie A after a terrible start to the season, on six points from three games.
They lead CSKA Moscow, who beat Trabzonspor 3-0 earlier on Tuesday, by two points, with the Turks and Russians on four and French champions Lille bottom on two points.
Lille dominated the match but were caught cold by Pazzini's strike and, despite fine performances by Eden Hazard and Joe Cole, lacked presence in the area to get on the scoresheet.
"I am very satisfied with my players. It's a first step. The whole team played with great discipline tonight," Inter coach Claudio Ranieri told a news conference.
"Until now, we were not too lucky but little by little some key players are finding their best form. This game will help us in the [Italian] league."
Lille captain Rio Mavuba told reporters: "We knew they [Inter] were not in great shape but they still have talented players. They came near our goal only twice but they scored.
"We did not really play our football in the first half. We were much better after the break but it's not enough for a Champions League game.
"There are still nine points to grab, we will have to collect some away from home now."
It was only Inter's second clean sheet of the season, their first since a goalless draw against AS Roma a month ago, as the visitors played cautiously throughout.
Cole was also in a class of his own on the left wing but Julio Cesar was quick off his line to collect the former England international's through-pass towards Moussa Sow.
The Inter goalkeeper then denied Sow again, diving at the Senegal striker's feet to nudge the ball away as the Italian side held on to claim the points.
