Girard's side drew 1-1 with Grasshopper in the Champions League's third qualifying round on Tuesday, advancing to the play-offs with a 3-1 aggregate win, but Lille almost let the Swiss visitors back into the tie after half-time in the second leg.
Florent Balmont had given Lille the lead in the first half with a thumping strike in front of their home fans, before Amir Abrashi equalised just after the half-hour mark.
Grasshopper's Moanes Dabour forced Lille goalkeeper Vincent Enyeama into a fine save after the break, while Mahmoud Soliman hit the post for the Swiss Super League club.
But after Grasshopper defender Daniel Pavlovic was sent off in the 68th minute, Lille were able to navigate their way to an aggregate win, although their coach was not too impressed.
"We had the opportunities to kill the game, but it wasn't to be and afterwards we were on the verge of conceding a goal and doubting," Girard said.
"We made a good start to the second half, then they hit the post and Vincent made a stop. We can do better. It still needs work...there has not been a lot of continuity in the game. I think over the two games [victory] is deserved.
"The lesson to be learned is that Europe is not simple, we must remain vigilant at all times and learn how to handle this kind of matches."
Lille must win one more two-legged tie to reach the group stage of the Champions League with the Ligue 1 club hoping to play in Europe's premier club competition for the third straight campaign.
