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."
TALENTED PLAYERS
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."
Lille, who led in their first two games but had to settle for draws after conceding late goals at home to CSKA and away to Trabzonspor, travel to the San Siro in two weeks time.
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.
They found the net with their first clear chance when Pazzini volleyed home from a Mauro Zarate cross.
MIDFIELD ENGINE
The goal spurred Lille into action, with Hazard turning on the engine in the midfield, making life a misery for the Inter defence with a string of devastating runs on the right flank.
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.
Inter were happy to sit back and wait, proving dangerous on the break with Zarate the main threat.
The hosts came into the second half with all guns blazing but lacked bite in the box, prompting coach Rudi Garcia to replace midfielder Benoit Pedretti with striker Dimitri Payet after the hour mark.
Payet had a clear chance in the 66th minute but his fine curled shot from just inside the area was palmed away by Julio Cesar.
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.
