The 2011 French champions needed an extra time goal on Wednesday to continue in the lucrative European tournament at the expense of FC Copenhagen in a game defender Franck Beria had labelled "the match of the year".
"It was important to qualify for the club and its future," goalkeeper Mickael Landreau said after the 2-0 victory over the Danes.
Lille, who signed France playmaker Marvin Martin and Ivory Coast forward Salomon Kalou this summer to make up for the departure of Eden Hazard to Chelsea, are widely regarded as the main challenger to PSG in this season's title race.
But the distraction of the European campaign has led to a disappointing league start. Lille could only draw 1-1 at home to Nancy ten days ago then relied on Landreau's superb performance to save a point at lowly Nice last weekend.
"Now we will focus on resting and have only the PSG game in mind," said coach Rudi Garcia, who had revamped his starting lineup at Nice to prepare for the European tie.
Sunday's clash will also be an important match for PSG, who lie 11th on three points from three games after two goalless draws in disappointing showings at Ajaccio and Bordeaux.
Defender Thiago Silva, one of the biggest signings of the summer, could make his debut at Lille after joining from AC Milan, while another recruit, Argentina forward Ezequiel Lavezzi, is serving the second of his two-match ban.
While PSG have endured a stuttering start, Olympique Marseille are enjoying a bright beginning, but the memories of their 10th-place finish last season have left them cautious when talking about their French title chances.
Marseille top the table on nine points from three games without conceding a goal and entertain European hopefuls Stade Rennes on Sunday (1500).
"We have to keep both feet on the ground and appreciate this situation because we went through hard times," defender Rod Fanni said this week.
"After the end of the season, we said to ourselves that it should never happen again. We have a new coach, a fresh spirit. Last season was an accident," added in-form striker Andre-Pierre Gignac, who has already doubled his tally from last season with two goals.
Second-placed Olympique Lyon, who lie two points behind Marseille, face Valenciennes, also on seven points, on Saturday (1500) without forward Lisandro Lopez who faces three weeks out because of injury.
Defending champions Montpellier, who are suffering their worst start to a season in 15 years with one point, travel to bottom-side Sochaux, the only team without a point. (Reporting by Gregory Blachier; Editing by Patrick Johnston)