The goal had been coming, sure. But to concede with so little time remaining in the first half seemed to compound the blow. Still, there were no panic substitutions at the break and United began the second period in positive fashion.
A succession of corners failed to yield a clear-cut chance, though, and Sir Alex switched to 4-4-2 just before the hour mark. Park was sacrificed for Danny Welbeck to provide United with more attacking impetus, but it was City who almost scored a second when Yaya Toure drilled a ball across the six-yard box and De Gea was forced to clear with his feet.
Welbeck's introduction succeeded in briefly penning City back and, sure enough, Mancini even withdrew one of his strikers (Tevez) and sent on a defensive midfielder (Nigel De Jong) in response. After gaining the upper hand, the Blues weren't going to relinquish it without a fight.
A loose pass by Rio Ferdinand on the halfway line allowed Toure to advance and shoot, but the Ivory Coast midfielder's effort flew past the post. Chris Smalling then produced a brave block to deny Carlos Tevez before a clumsy De Jong tackle prompted ugly scenes on the touchline where Mancini and Ferguson had to be separated.
The incident proved just how high emotions run in this fixture and served as a reminder of exactly what's at stake. A championship, that's what. And unless City now slip up in either of their next two fixtures, the Reds will surely be left to rue recent results and what might have been. If there's one thing Manchester United have taught us down the years, though, it's never to give up.