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.
After the victory, the Arsenal boss was quick to praise his team and the impact Lacazette made on his Premier League debut.
Alexandre Lacazette got his and Arsenal's season off to the ideal start with a debut goal in the first two minutes.
It was the ideal way to seal an enthralling game that had threatened to end in defeat for the home side.
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Gabriel Jesus's arrival has given him competition but expect him to feature in the starting XI more often than not. That Walker has been one of the best full-backs in England for the last couple of seasons was never up for debate.
Arsenal weren't celebrating for long because just 160 seconds later, Leicester had equalised through Shinji Okazaki. The guests capitalised on the abundant mistakes from Arsenal players and their sloppy defending as Jamie Vardy eventually made it 2-1 from Marc Albrighton's cross around the half-hour mark. Arsenal were shell shocked. The away side shut up shop at this point, and for the next 25 minutes the home side met a thick blue line every time they tried to get into the box.
Vardy scored again in the second half before much-maligned manager Arsene Wenger would make two critical substitutions, bringing in striker Olivier Giroud for Rob Holding and Aaron Ramsey to replace Mohamed Elneny with just over 20 minutes left in the game.
Before that though, Vardy stunned Arsene Wenger's men with two goals and Shinji Okazaki also went on the score sheet to nearly punished Arsenal which played without star forward Alexis Sanchez because of injury.
It was an incredible escape act from Arsenal, but Giroud claimed his team, who dominated possession and peppered the Leicester goal, never doubted they would hit back. The Welsh worldwide took one touch before putting an exquisite shot across Kasper Schmeichel.
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It was the Frenchman's 26th headed goal since he signed for Arsenal in June 2012, a Premier League record.
Lacazette slipped as he went to turn and shoot and scuffed his shot to Kolasinac, who found himself one on one with Schmeichel. He netted the victor after fellow substitute Aaron Ramsey had equalised past the hapless Kasper Schmeichel.
With eight minutes remaining Ramsey did find the equaliser for Arsenal after being set up by Xhaka.
One of these players is Leicester City's Danny Drinkwater, who partnered N'Golo Kanté during Leicester's Premier League-title winning campaign back in the 2015-16 term. "Overall we showed great character in the first game of the season - we played a classic".
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Out: Santi Cazorla (ankle), Laurent Koscielny (suspended), Alexis Sanchez (abdominal), Gabriel (knee). We are going to see at the end of the season what happens, knowing how hard it is".
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