With Arsenal having led 2-0, thanks in part to a goal from returning contract rebel Walcott, the brittle self-belief of the players was again evident as they subsequently wilted under sustained Schalke pressure.
Ultimately, though, there will also have been some relief at the final 2-2 scoreline, a result that still leaves Arsenal sandwiched between Schalke and Olympiakos at the top of a congested Champions League Group B table.
After being beaten with such ease on Saturday by Manchester United, Wenger made the two changes that most supporters would have been hoping for. Out went Andre Santos and Aaron Ramsey, with Laurent Koscielny and Theo Walcott respectively adding pace to both the front and back of the team. Santos had apologised to his team-mates for bizarrely swapping shirts with Robin van Persie at half-time of Arsenal's 2-1 defeat against Manchester United on Saturday but the decision to omit him was made on purely footballing grounds.
In the corresponding fixture two weeks ago, Santos had been horribly exposed at left-back by Atsuto Uchida and Jefferson Farfan. In an attempt to stabilise that area of the pitch, Wenger shuffled captain Thomas Vermaelen to left-back and reunited Koscielny with Per Mertesacker at centre-back.
The tactic had little initial success in negating Uchida and Farfan, with Schalke pinning Arsenal inside their own half and creating three clear chances in the opening 12 minutes. From Farfan's corner, Benedikt Howedes was permitted space inside the Arsenal penalty area but headed narrowly over.
Ibrahim Afellay, a transfer target of Arsenal, looked full of confidence in the early stages, testing goalkeeper Vito Mannone with a powerful shot low to his right.
Schalke's third opportunity to take the lead arrived after Walcott had been dispossessed deep in the German club's half. Four quick passes followed, with Klaas-Jan Huntelaar cleverly teeing up Christian Fuchs, only for his shot to be blocked by Mikel Arteta.
With Arsenal still apparently just trying to survive Schalke's initial storm, the game turned on two crucial moments. Uchida, who had been so effective at right-back, pulled up injured and had to be replaced, depriving Schalke of one of their main attacking outlets.
Roman Neustadter also then committed a dreadful individual error, misdirecting an attempted headed clearance that inadvertently put Giroud clear on goal. The France striker hesitated with the goal at his mercy. Walcott, though, was following up and, with the ball cannoning off Unnerstall and into his path, he calmly put Arsenal into the lead.
Arsenal looked like a huge weight had been removed from their shoulders and, eight minutes later, found the attacking fluency that has so defined the past 16 years under Wenger. Giroud dropped deep to collect Jack Wilshere's pass and then released Lukas Podolski wide on the left. The German delivered a precise return cross. Giroud had timed his run perfectly and, in evading Joel Matip, clinically produced Arsenal's first headed goal of the season.
Schalke, the Champions League semi-finalists in 2011, responded strongly and placed Arsenal under further sustained pressure. Farfan remained a persistent threat but, when he wasted one excellent chance in the 42nd minute, it appeared that Arsenal would survive unscathed until half-time.
Walcott, though, lost possession with just seconds of the half remaining, allowing Schalke to mount a rapid counter-attack that ended with Lewis Holtby heading into the path of Huntelaar. Mertesacker had been dragged out of position, allowing Huntelaar to punish the mistake with the sort of deadly finish that made him the Bundesliga's leading scorer last season.
As the two teams entered the tunnel, Wenger approached Nicola Rizzola, the Italian referee, to complain furiously that Walcott had been fouled in the lead up to the goal.
Wenger had further cause for concern at the beginning of the second half when Wilshere went down clutching his ankle. The England midfielder initially looked in considerable pain, prompting fears of a setback on his return to fitness following 14 months out.
Treatment followed and, to the relief of a vocal away contingent, he got back to his feet and resumed the game. Wilshere, though, appeared jaded and, with Schalke threatening to overrun Arsenal's midfield, a flurry of further chances followed. Arsenal surviving a loud penalty appeal as Neustadter's shot was driven towards the arm of Mertesacker.
Further last-gasp defending was then required when Arteta, who was guarding Arsenal's post from a Schalke corner, blocked Marco Hoger's shot.
An equaliser was becoming inevitable and, shortly after Holtby had forced another save from Mannone, the pressure eventually told. The weakness to Arsenal's left was again evident as Farfan drifted into a huge swathe of space on the edge of the penalty area. He opted for power rather than precision and, in smashing his shot across the Arsenal six-yard box, Vermaelen was unable to control his attempted clearance and the ball was deflected past Mannone and into the goal.
Schalke had most of the subsequent chances to secure victory but the best opportunity fell to Walcott in the final seconds of the match.
His pace had got him behind the Schalke defence but his shot was blocked by the legs of Unnerstall.