Arsene Wenger got the response he wanted as Arsenal bounced back from turmoil to defeat Manchester United 2-1 thanks to a double from Samir Nasri.
Gunners manager Wenger admitted dressing-room morale was low after their 4-4 draw with rival Tottenham and the defeat at Stoke - but this win at the at the Emirates Stadium breathes life into their campaign and lifts them above United in the Premier League.
Wenger had Emmanuel Adebayor injured and Robin van Persie suspended but Nasri provided the attacking threat, taking advantage of slack marking in each half to grab his fourth and fifth goals of the season.
Rafael da Silva, on as a substitute, volleyed home a late strike to give Sir Alex Ferguson's men hope - but there was no repeat of the memorable Spurs comeback.
It was Arsenal's first test this season against their traditional top-four rivals - and Wenger's men passed with flying colours.
This clash between two heavyweights had everything - chances, yellow cards, counter-attacking and also four penalty shouts.
Referee Howard Webb, who was kept busy throughout, turned down appeals when Dimitar Berbatov was bundled over by Denilson, as well as when Gary Neville and Gael Clichy touched the ball with their arms.
Then in the second half, Nasri appeared to be bundled over by Nemanja Vidic.
Between those moments, there was absorbing end-to-end football, with United given an early opportunity following a mix-up involving one of its former players.
Mikael Silvestre clipped a backpass to Manuel Almunia and the goalkeeper picked up the ball. Anderson's free-kick was blocked by team-mate Ji-Sung Park, then Michael Carrick fired the rebound wide from the edge of the area.
Berbatov also had the ball in the net but was ruled offside when he followed up Rooney's shot.
Then it was Arsenal's turn to attack. Nicklas Bendtner headed over from Clichy's cross, before the striker was millimetres away from contact when Nasri swung a ball over.
Abou Diaby had a clear sight of goal when Edwin van der Sar flapped, but his effort was blocked by Carrick.
United took its turn to apply pressure, with Cristiano Ronaldo raiding down the flanks and Carrick creating his angles in midfield.
Wayne Rooney was guilty of wasting the clearest opportunity of the opening period when he flashed a shot over after Ronaldo's intelligent pull-back.
First blood went to Arsenal, with Nasri's opener coming midway through the first half after Patrice Evra fouled Bacary Sagna on the right touchline.
Berbatov headed away the free-kick as far as Nasri, who fizzed a volley at goal that took a deflection off Gary Neville to wrong-foot Van der Sar and fly in.
United almost replied when Clichy only just headed wide of his own goal as he tried to clear a free-kick. William Gallas had been booked for his trip on Evra to lead to the set-piece.
Arsenal, meanwhile, tried to counter-attack and Cesc Fabregas shot just wide of the post with one effort, while Van der Sar stuck out a hand to stop Silvestre stabbing home from a corner.
The intensity, already sky-high, stepped up a level before the break and Evra and Sagna both received yellow cards from Webb.
Nasri's second came three minutes after the restart.
Fabregas wriggled around Neville and spotted Nasri unmarked on the penalty area, with the France youngster given enough space to bide his time and lash past Van der Sar.
Ronaldo was presented with