Arsenal put their recent troubles behind them to beat Borussia Dortmund 2-0 at the Emirates Stadium and qualify for the knockout stages of the Champions League with a match to spare.
The Gunners have endured their worst start to a domestic campaign for 30 years, and are eighth in the Barclays Premier League following Saturday's 2-1 home defeat by Manchester United.
However, Arsene Wenger's men produced the perfect response as Yaya Sanogo scored inside two minutes, with Alexis Sanchez clipping home a sublime effort at the start of the second half to inflict a first European defeat on the Group D leaders – who could still be caught for top spot should results go the Gunners' way on matchday six.
With Danny Welbeck out injured and fit-again Olivier Giroud not registered for the Champions League squad, Wenger had opted for Sanogo ahead of German international Lukas Podolski, who again had to make do with a place on the substitutes' bench.
Wenger's faith was rewarded as Sanogo took just 73 seconds to fire the Gunners ahead, when he stabbed his shot under goalkeeper Roman Weidenfeller.
The France Under-21 forward, who has suffered a string of injury problems since signing from Auxerre in 2013, spurned a chance to add a second when he sprinted clear, only to be crowded out as the Dortmund defenders covered back.
Dortmund, who had won all four European ties despite poor Bundesliga form, slowly got a foothold in the match, but for once this season Arsenal's defence looked solid enough as the damp mist descended on north London.
In the 38th minute, Emiliano Martinez – the third-choice goalkeeper in for injured Wojciech Szczesny, who picked up a hip injury when conceding the opening goal during the 2-1 Barclays Premier League defeat by Manchester United – produced a smart reaction save with his feet to deny Henrikh Mkhitaryan.
At the start of the second half, Weidenfeller denied Sanchez with a low stop down to his left.
Alex Oxlade-Chamberlain was then unfortunate to see his sublime 25-yard volley drop back off the crossbar.
Weidenfeller was, though, beaten again when Sanchez curled in a brilliant second goal on 57 minutes, cutting inside from the left.
Oxlade-Chamberlain, so impressive for England during the friendly win over Scotland in Glasgow, continued to stretch the Dortmund defence, drilling an angled shot just over after cutting in from the right.
Sanogo's injury jinx struck again when he hobbled off with a hamstring problem, replaced for the final 12 minutes by Podolski, who got a rousing reception from both sets of fans.
Martinez preserved a clean sheet when he saved with his feet at point-blank range from Ramos in stoppage time.
Arsenal – also without Jack Wilshere, whose ankle ligament injury could yet require surgery – had swept ahead inside two minutes as Sanogo grabbed his first senior goal for the club.
Sanogo, who was on target for France Under-21s during the international break, had his back to goal at the edge of the area, but flicked the ball up and out to Cazorla.
The Spaniard jinked inside his marker before sliding a pass through to Sanogo, who just about held onside to slot home from inside the six-yard box.
Dortmund – who held an impromptu "pre-warm-up" training session in the pitches at Regent's Park earlier on Wednesday – soon regrouped and Lukasz Piszczek almost found Ciro Immobile at the far post, before Martinez showed good reactions to get his foot on a low shot from Mkhitaryan.
Arsenal – who had squandered a 3-0 lead against Anderlecht here a fortnight ago – pressed at the start of the second half, with Sanchez forcing Weidenfeller into a strong-handed low stop down to his left after the Chile forward muscled his way into the Dortmund penalty area.
Three minutes after Oxlade-Chamberlain struck the bar, Sanchez doubled Arsenal's lead.
Dortmund had needed just a point to win the group, and manager Jurgen Klopp, who harbours ambitions of coaching in England one day, made a double change on the hour.
Immobile was replaced by Shinji Kagawa, the former Manchester United player, while Adrian Ramos came on for Aubameyang.
Arsenal were then forced into a change when captain Mikel Arteta, who had just come back from injury, hobbled off with Mathieu Flamini his replacement.
Sanogo pulled up with a hamstring problem and could not continue, so Podolski came on for the closing stages.
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