Wayne Rooney's 100th club goal was enough for Manchester United to confirm local supremacy over City at Eastlands - but Cristiano Ronaldo did not help with a red card.
Ronaldo was sent off midway through the second half, after receiving his second yellow card for a deliberate hand-ball in the box.
Already booked, referee Howard Webb duly produced a second yellow card, condemning United to a nervy finish in which Patrice Evra cleared off the line from Richard Dunne although Joe Hart also denied Rooney seconds later.
It meant Rooney's first goal for a month turned out to be the matchwinner, allowing United to record the third away win of the season in the Barclays Premier League.
This is a different derby now, with City's vast wealth making this a fixture which is sure to be even more keenly fought in the future than it has been in the recent past, with British record signing Robinho the symbol of the new cash-rich Blues.
Not that the Brazilian was involved to any great extent during the opening period.
Apart from sliding in on Edwin van der Sar with a challenge that was fortunate to escape added punishment and a free-kick that did not threaten the United goal, he was a bystander.
He was not involved in City's best first-half chance, which came as a result of Van der Sar's weak punch just after the half-hour.
too hot
Stephen Ireland lofted the loose ball towards the empty net. Micah Richards, thinking it was going in, opted not to try and divert it past Evra and turned away in disbelief as it bounced to safety off the outside of a post.
Apart from that, it was all United.
United's record signing Dimitar Berbatov was unfortunate when Hart made a superb one-handed save to deny him midway through the opening period. But the Bulgarian was also off-target with a decent opportunity, as were Rooney, Cristiano Ronaldo and Evra.
Sir Alex Ferguson must have been preparing for a familiar half-time team talk when Ireland fouled Evra, offering another opportunity for the visitors to cause some damage.
Park Ji-Sung was heavily involved as United threatened City's penalty area.
But the ball eventually broke to Michael Carrick, whose stinging angled drive was too hot for Hart to hold. Stationed alone, inside the six-yard area, Rooney could not miss, reaching three figures in a career that began in such explosive fashion for Everton against Arsenal when he was just 16.
Mark Hughes' response was to introduce Elano and Pablo Zabaleta, which immediately brought more attacking threat from his team.
heating up
Pushed into midfield, Vincent Kompany tried his luck from 25 yards before Shaun Wright-Phillips, identified as a danger man given the way he was buffeted around, fed Benjani Mwaruwari whose first-time shot struck the side-netting.
There was no let-up in the intensity of the tackling as Robinho, Ronaldo, another peripheral figure, and Evra got up gingerly.
Elano wasted a free-kick by ballooning it into the stand but then Robinho himself did no better, rolling a quickly-taken effort into space he expected Benjani to fill when the Zimbabwean had not actually made a run.
If the atmosphere was heating up, it positively boiled over when Ronaldo left United to complete the final 22 minutes with only 10 men.
Ronaldo had left Webb with little alternative than to show a second yellow card for deliberate handball as he leapt for Rooney's corner. It was the second time he had been dismissed on this ground, having also seen red in January 2006.
Ferguson must have been tempted to make a change but when the substitution arrived, it came from City in the form of Daniel Sturridge as United sat back, soaked up possession and, eventually, collected a win.
