It now leads the French top flight with 69 points from 32 games while PSG has 63, Monaco 62 and Lyon 61 ahead of their catch-up games this weekend.
Turkish veteran striker Burak Yilmaz got the opener on the hour and compatriot Zeki Celik scrambled home a second at the death after Lille goalkeeper Mike Maignan had saved an early Metz penalty.
"We had a very sluggish start to the match," Lille coach Christophe Galtier admitted.
"We struggled to get the ball out. The desire to do well made us rush and we were wasteful. Mike kept us in the game by stopping the penalty."
Yilmaz showed great experience, wrong footing the Metz keeper and shooting hard and low inside the near post to score.
Celik scrambled home a corner on 89 minutes to provide a harsh scoreline for the hosts.
Maignan saved a 17th-minute penalty, diving low to turn Aaron Leya Iseka's spot-kick round the post.
This came after John Boye's volley for Metz was goal-bound but stopped on the line by defender Jose Fonte, who raised an arm to protect his face.
After an impressive 3-2 UEFA Champions League win at Bayern Munich midweek, PSG will next play Strasbourg on Sunday (AEST), hoping to keep up its push for a fourth straight title.
Monaco hosts Dijon and Lyon welcomes Angers.
Christophe Galtier's Lille emerged as a strong contender for the title last weekend by stunning PSG in the capital.
Lille was second in Ligue 1 to PSG in 2019 and was fourth last season, when the championship was curtailed because of the coronavirus pandemic.