Paris Saint-Germain were the only other title contenders to keep up with the pacesetters after earning a 2-1 win at bottom club Arles Avignon courtesy of a Mevlut Erding double.
Lille have 41 points from 21 games ahead of second-placed PSG on 37 with Olympique Lyon and Stade Rennes on 34 after both lost away with the latter going down 5-1 at mid-table Sochaux.
Saint-Etienne climbed to sixth on 32 points thanks to a 2-1 home victory over Toulouse who slipped to seventh.
At Stadium Nord, Lille dominated the northern derby against Lens but could find a way past Lens's Croatia goalkeeper Vedran Runje until the 70th minute when De Melo found the back of the net with a celver volley from a Ludovic Obraniak cross.
"We get along really well with Tulio," Obraniak told French TV channel Orange Sport. "It's my role to set him up. Tonight, it paid off. And the other teams' results were favourable to us, so tonight was a really good night."
After two straight wins, Lens have slipped back into the drop zone with 22 points.
RENNES SLUMP AT SOCHAUX
At Arles-Avignon, PSG's previously out-of-form Turkish striker Erding scored a goal in each half before Deme N'Diaye reduced the arrears for the hosts, who have just eight points from 21 games and are 15 points adrift of the safety zone.
Claude Puel's Lyon suffered a 2-1 defeat at Valenciennes, their first in Ligue 1 in four months but their second in a row after their French Cup exit to Nice last weekend.
Valenciennes took the lead in the 51st minute with a Milan Bisevac penalty before Gregory Pujol made it 2-0 seven minutes later. Lyon's Brazilian striker Michel Bastos pulled a goal back in the 71st but they were unable to salvage a point.
"I hope this result can trigger something good for us", said Valenciennes coach Philippe Montanier on French TV channel Foot Plus. "Until now we hadn't been rewarded for our efforts. It gives us hope for the rest of the season." Valenciennes's win took them up three places to 13th.
Rennes slipped one place to fourth on goal difference after being thrashed at Sochaux where they finished with 10 men.
The Bretons were losing 3-1 when goalkeeper Nicolas Douchez was sent off for bringing down striker Modibo Maiga, who had opened the scoring, and conceded a penalty with 15 minutes left.
With Rennes having already used all their three substitutes, midfielder Alexander Tettey went in goal and narrowly failed to save Ryad Boudebouz's spot-kick before Maiga added the fifth.
