Julian Alvarez had Atletico ahead early before Lille fought back through Edon Zhegrova, plus a brace from Jonathan David - his first from the penalty spot.
Oblak later admitted frustration over the penalty call.
The penalty:
"I don't know, he said it was a handball, but in the end I don't know what he called. Nobody understands, I hope he understands. We can't complain about him, because we had chances to finish the game and then they scored from the penalty spot, from a rebound... In the end it was very ugly, because you lose 1-3 at home, but we didn't finish and they punished us."
Lack of success:
"When you score more goals it's easier, because anything can happen in the game, as has happened, a shot, someone touching the ball... They shoot three times and score three and we score more and score one. Now everything looks very ugly, but if we had scored it would be different."
Has Koke told you something about the penalty:
"We talked about the handball, he called a handball and in the end I don't know what happened. He said that they were checking the handball and if it wasn't a handball, I don't know what it was. It's incredible. But, as I said, it hurt us, although if we had done the job, this error couldn't have punished us."
The handball belongs to the Lille player?
"What I know is what he told us. That they were checking the handball. I don't know what happened. They will give explanations..."
There is little room for error in the Champions League:
"After losing, we should have won today. We didn't do it and of course there are still games left and we have to win, but we also said that after the game in Lisbon and we lost at home. We have to hold our heads up high and win the games."