United might have been fortunate to survive a late Villa penalty appeal when John Carew went down under Jonny Evans' tackle, but it would have been harsh luck on Sir Alex Ferguson's men, who will regard it as a point gained rather than two lost after James Collins scored another own goal for United to cancel out Carlos Cuellar's opener.
In the build-up, Nani had spoken about how down he felt at times during his first two and a half years at Old Trafford, when it appeared his destiny was only to leave.
The past fortnight offered the hope of redemption as finally the pace and balance was accompanied by a bit of thought and composure.
But thought and composure were both lacking when the winger launched himself at Petrov on halfway a minute before the half-hour mark. The former Sporting Lisbon wide-man is not a dirty player and did win the ball but both his feet were off the ground.
Referee Peter Walton was near enough to make a judgment and duly despatched Nani to the dressing rooms and rule him out of the Wembley showpiece between these sides on February 28.
It brought to an end a tactical opening half-hour which Villa led for precisely four minutes after taking the lead on 19.
After wasting a corner, Stewart Downing was offered a second chance to cross into the United box. Rafael stuck out a boot to make the initial clearance but the ball looped up handily for Cuellar, who got an impressive amount of power into his header and, from 15 yards, sent it arcing over Edwin van der Sar.
Following their first Old Trafford win since 1981 two months ago, Villa were now in position to end another long-running sequence against the Red Devils.
Yet this is not Ferguson's favourite away ground for nothing.
Even though their fans now twirl green and gold scarves above their heads as a continuing protest against the Glazer family, the United travelling support still makes an impressive noise.
And they were soon celebrating an equaliser as Ryan Giggs' cross-shot from the left - after he had been found by Nani - was turned into his own net by Collins.
It took into double figures a quite staggering number of own goals for United this term - a clear second on the club's scoring chart and nearly half as many as Wayne Rooney.
The England star had been having one of his less effective days, yet he still managed to threaten the home goal with shots from both angles that fizzed over Brad Friedel, who had already saved well to deny Michael Carrick.
With the balance of play remaining with the visitors, it was hard to escape a conclusion that Villa would have preferred to be playing against 11 men, whose defences were rather less solid.
For all the plaudits that have been heaped on Martin O'Neill's men in recent times, dictating play is still a problem and the hosts were markedly less of a threat once their opponents were a man down.
The loss of Giggs to what appeared to be a pretty severe elbow injury could have dire consequences for next Tuesday's Champions League trip to AC Milan.
Rooney's shot shortly afterwards would have had dire consequences for Villa if Friedel had not acrobatically turned it over.
Villa finally shrugged off their lethargy for a concerted assault on the United goal in the final 10 minutes.
But apart from an untimely Van der Sar juggle and Carew's late penalty claim, the hosts were bereft of ideas, and United were probably irritated they did not head back up the M6 with more than a point.