A month ago, when Manchester United lost 3-1 to neighbours City, the Premiership title looked a distant dream.
But that game proved a watershed and United has since been firing on all cylinders in all competitions with this comprehensive win over champions Arsenal throwing the title race wide open.
United out-fought, and out-fired the Gunners. When Arsenal clinched the title at Old Trafford near the end of last season the balance of power looked to have shifted southwards.
But United,as so often in the past, have shown unbridled powers of resilience. Roy Keane, Rio Ferdinand, David Beckham and Nicky Butt all looked on as goals by Juan Sebastian Veron and Paul Scholes clinched a deserved victory.
Veron, so often looking more like a misfit than a footballing magician since his £28million siging from Lazio 18 months ago, glided along effortlessly as his orchestrated the Red Devils from midfield.
Alongside him, Phil Neville played with Keane-like zeal to deny Arsenal time to settle on the ball.
In defence, United were unshakable with Wes Brown and Mikael Silvestre providing a solid centre and Gary Neville and John O' Shea flexibily secure on the flanks.
In a game of few clear chances United almost drew first blood in the ninth minute when Arsenal goalkeeper Rami Shaaban superbly turned behind Ruud van Nistelrooy's fierce 20-yard drive.
Arsenal's best chance of the game came three minutes later. Thierry Henry beat United's offside trap to collect Oleg Luzhny's pass on the edge of the United box. But with only Fabien Barthez to beat, he hurried his shot, enabling the United goalkeeper to make a fine save from point -blank range.
It was Veron who made the vital breakthrough for United in the 21st minute. Pascal Cygan's header out of the Arsenal defence was collected by Scholes on the right.
His ball to the edge of the Gunners box was controlled by van Nistelrooy with a mixture of arm and chest before he returned the pass to Scholes.
The England star took the ball on to the right edge of the penalty area before whipping in a low cross which was despatched into the net right-footed by Veron from six yards.
Arsenal lost Shaaban with a knee injury in the 43rd minute and United's control of the game grew after the interval.
In the 72nd minute, van Nistelrooy fed Scholes from the right and his glorius side-step took him away from Arsenal defender Martin Keown and allowed him to score with a deflected right-foot shot from 12 yards.