The lead lasted three minutes before Leicester's new signing Harry Maguire headed Marc Albrighton's cross from the left back into the middle and Shinji Okazaki nodded the ball past flailing Arsenal goalkeeper Petr Cech.
Lacazette almost had his second of the night just minutes later, but Leicester keeper Kasper Schmeichel turned the shot aside, but Giroud beat the Dane with an exquisite header on the ensuing corner to give Arsenal the 4-3 victory.
Wenger shuffled his pack and Aaron Ramsey levelled with eight minutes remaining before fellow substitute Giroud wrapped up the points.
That excitement was immediately transformed into celebration not two minutes into Lacazette's Premier League debut, as he bagged a pinpoint header to put the Gunners on top of Leicester City in the opening match of the new season. At some stage, I opened the door for him because I knew that I had many strikers.
"He doesn't want to leave and I'm happy he wants to stay".
Manager Arsene Wenger this week revealed that he gave the player the option of leaving, but that he chose to fight for his place.
"Lacazette is simple. In every game he is stronger since he has joined us", Wenger said.
"I went to a three-man midfield to get us a screen because Mesut Ozil was playing in the pockets and I wanted Wilfred Ndidi to get in and around him. Overall I must say we kept going and the spirit of the team was absolutely outstanding and overall you could say as well we were punished on every single mistake tonight by a Leicester team who was very efficient going forward", Wenger said after the win, as quoted on Arsenal's official site.
"Previously in the Premier League we've not got off to the best of starts, so it meant a lot for us to get a good start and get three points today".