Neil Humphreys: United can challenge City only if they play this way
United boss has no choice but to attack now
No wonder Jose Mourinho couldn't stop rubbing his forehead in the post-match interview.
He's caught in a conundrum of his own creation.
He must defy every impulse, every internal screaming voice of negativity and follow a new path, the only road to Old Trafford.
There's no other way for Mourinho now, not after that 45-minute shellacking at the Etihad, that euphoric silencing of the neighbours.
One half of football offered both a throwback to United's glory days and a defiant repudiation of the current set-up.
United's second-half performance in their 3-2 win wasn't a Mourinho performance, but an exhibition of anarchic artistry. They looked to the future by stealing from their past.
Take Paul Pogba's first goal. He connected near the six-yard line. He collected a chest-down from Ander Herrera, who lurked around the penalty spot. Two red jerseys were in the box with others for company.
This was Sir Alex Ferguson's United, a tsunami of attacking momentum.
David Moyes and Louis van Gaal had gone the other away, leaving the club swimming against the tide of public opinion. Mourinho relented, a little, and even picked up the League Cup and Europa League trophies. He still believes that caution guarantees cups.
But Pep Guardiola's slavish devotion to devastating attack left Mourinho behind. The first half of the Manchester Derby proved that. United didn't manage a single shot at goal. City conjured nine. Only Raheem Sterling's indecisive finishing prevented a rugby score.
This was Mourinho's United writ large; the bus-parking United at Anfield, the cautious United against Sevilla, the confused, disjointed United following a lost leader.
Who made the decision to go for broke in the second half is a matter of conjecture. Did Mourinho really instruct his deflated charges to do a City on City?
Or did his shackled players take it upon themselves to tear off the restraints?
It really doesn't matter. It worked. And United, like Liverpool, demonstrated that a soft underbelly remains between City's centre-backs. Push them around in the penalty box. They may fall over.
But they must be attacked first, endlessly and mercilessly. Pogba, Herrera, Nemanja Matic, Jesse Lingard and Alexis Sanchez, so anonymous in the first half, pressed forward with an invigorating sense of purpose.
Attacking confidence flowed through the side in a fashion not witnessed since the final days of Ferguson.
TOO BIG TO PLAY SAFE
United looked like scoring every time they attacked. It was retro. It was wonderful. It was hopeful for the rest of us.
United can challenge City's billionaires next season, but only if they play like this.
After the game, Mourinho was eager to play down the victory. City will still swagger to the title, he said, the gap remains huge and so on, relying on those broken records to perhaps avoid mentioning his broken system.
As long as Guardiola stays with City's oligarchs, Mourinho's conservatism will never prevail across 38 games.
He'll always have his little victories. He held Barcelona at Inter Milan. He stopped Liverpool winning the title in 2014 by parking a fleet of Chelsea buses. This season, he left Anfield with a clean sheet. He beat Tottenham at Old Trafford. But those brief moments of validation felt like petty battles, small incidents in a war he can no longer win. The game has moved on.
The second half at the Etihad, however, offered a glimpse of something else.
Whether by accident or design, United unveiled an optimistic, engaging template that could potentially take down City.
It's certainly not foolproof. Like Guardiola in pre-season, Mourinho needs a couple of defensive reinforcements to breed confidence in midfield. Then he can unleash the beasts of Pogba, Matic and Sanchez and take the battle to City.
That's the real pay-off for Mourinho's men; a clear mandate for tactical change. Never mind nonsense about "bragging rights". United are too big to obsess over bragging rights, just as they are too big to play safe.
The Red Devils' triumph in the Manchester Derby was to remind their manager of their underlying attacking ethos.
United can be so much more than underdogs next season, but only if Mourinho takes off the leash.