Abraham opened the scoring in the 22nd minute with a fantastic turn and finish, but Lille pulled level 11 minutes later through a header from Victor Osimhen.
However, Willian grabbed the winner in the 77th minute with a thumping volley following a cross from substitute Callum Hudson-Odoi.
After the game Abraham – who turned 22 on Wednesday – said he was hardly surprised to see his Brazilian team-mate score a tremendous goal to win the game.
"We knew we needed to win. I knew I would get a chance and I took it well. Never an easy place to play and Willian scores a worldie – no surprise there," Abraham told BT Sport.
"The manager always wants to mix things up, we can play any system. This is massive."
Willian was also happy to secure a win on a night in which he made his 300th appearance for Chelsea.
"We needed to win, we have been working hard and the lads did an amazing job," the Brazilian told BT Sport. "Now we have to carry on."
Chelsea have now won three consecutive games in all competitions, and their manager Frank Lampard was happy to see his side bounce back from a difficult defeat to Valencia.
"It feels really good," Lampard told BT Sport. "This was a really hard place to come, added to the pressure of not beating Valencia. And it was the first time for a few travelling in Europe."
One of those players making their first Champions League away appearance was Fikayo Tomori, and Lampard was pleased with how his 21-year-old defender responded to the occasion.
"Fikayo Tomori was outstanding again," Lampard said. "He has to keep on with that."
Next up in the Champions League for Chelsea is two straight games against Ajax, who are top of Group H after winning both of their opening two fixtures.
"Now Ajax have set their stall out in the group," Lampard said. "This gives us confidence and points. Now the hard work begins."