Les Dogues made it 11 consecutive Ligue 1 match with a clean sheet after holding out against an attacking Les Phoceens for the duration of the match, before Nolan Roux headed in the winner in stoppage time for a 1-0 win at Stade Pierre-Mauroy.
"It was a pretty closed match, especially in the first half, but the second was more open," Girard told reporters.
"Vincent [Enyeama] once again made some decisive saves. He's one of the keys to our current success. We were headed for a nil-all draw but we kept believing right to the end, and we scored.
"It's unfair for Marseille, but that's how it goes. Perhaps we were lucky and hit the jackpot, but in football anything can happen. We need to make the most of the good moments because there will surely be bad ones to follow. We need to stay humble and stay focused."
Lille are second in Ligue 1 and just a point behind leaders Paris Saint-Germain having played a game more.