The Ligue 1 side were beaten 1-0 by Porto in the opening leg of their play-off last week, with Hector Herrera's 61st-minute strike the difference in France.
Lille struggled to assert any kind of dominance on home soil against the Portuguese giants, who enjoyed 59 per cent of possession.
The win - which extended Lille's unbeaten streak in the league to three games - should hold the French club in good stead at the Estadio do Dragao on Tuesday, according to Girard.
"We know what we have to do. We lost 1-0 at home, so let's be effective, "Girard told reporters.
"I have confidence in my group. It will be 150 per cent for a successful outcome. Our victory against Lorient brought more confidence and changed the look on us.
"We know that we have a difficult task ahead. But we are competitors and will not let go of anything."
Girard added: "We could have done better, but we had a large calibre opponent.
"I still believe we can do something. We did not come to pass the time. There is a qualification for the group stage of the Champions League at stake. We have more to gain than lose."
