Substitute Aaron Ramsey rifled home to level before Giroud - introduced alongside the Wales global - headed in an 85th-minute victor to settle a breathless encounter in Arsenal's favour.
When Olivier Giroud came on for the last quarter, Lacazette was pushed wide and not only did he look comfortable out there but he didn't look like he was bothered that he was playing wide and handing the central role to Giroud.
"I opened the door for him at some stage because I know it's important for him to play..."
"There was something in my soul and in my heart which told me to stay", the French global is quoted as saying by the Daily Star. "I know how important he is not only as a player but also in the group".
Ronald Koeman's Everton have been most heavily mentioned in connection with the £25m-rated 30-year-old, with the likes of West Ham United, Marseille and Lyon also credited with an interest. He adapts slowly to the way we want to play.
When they were down 3-2, Wenger brought Giroud on, to play alongside his countryman, to impart some real firepower to the Gunners up front.
After undergoing solid preparation for the EPL opener, including beating Chelsea in the Community Shield, Arsenal were expected to start the season in a serene manner - score a couple of goals, make that back three look solid and pick up the three points without too much fuss.
But Welbeck had the last word of the first half for the home side when he equalised from close range in added time after new signing Sead Kolasinac's tap forward in a goalmouth melee. With Watford hosting Liverpool for the first game this evening, all eyes will be on Mohammed Salah who made his move to the Merseyside this season from AS Roma.
However, despite his impressive display during the match, the Ox's efforts seemed to go pretty unnoticed and has been hardly mentioned in match reports or commentary of the match.
"I love the man and the player [Giroud] and he doesn't want to leave and I'm happy that he wants to stay. Riyad has been very focused".