The Frenchman admitted that the incident occurred too quickly to recall in detail, but said that his finish was instinctive.
"It all happened so quick. I saw the ball and it was in the goal. I just do what I have to do when I get chances. I didn't have chances this season but tonight I took it," he told ITV Sport.
Chelsea progress to the last four of the competition 3-3 on the away goals rule following a 2-0 victory over the French giants at Stamford Bridge.