Premier League - Bent downs City on Villa debut
The striker, who joined Villa from Sunderland earlier in the week for a fee that could rise to £24 million, struck midway through the first half to begin justifying the large fee which has drawn criticism from some quarters.
Villa sealed the much-needed victory - their first win in six matches - thanks to a sterling defensive effort lead by former City captain Richard Dunne.
Having started the day out of the relegation zone on goal difference alone, Villa move three points clear of 18th-placed Wigan Athletic.
City enjoyed most of the possession but, despite an attacking quartet worth more than £100m, they had great difficulty in breaking through Villa's defence.
The visitor's best weapon in the first half was the deliveries of full-back Aleksandar Kolarov, who sent in a multitude of dangerous crosses and set pieces.
The closest one of those dead balls came to bearing fruit was a 17th-minute corner which swung through to Carlos Tevez, but the City captain somehow let the ball sneak through his legs as he tried to steer it home from close range.
The frustration over that spurned chance was compounded moments later when Villa broke forward. Ashley Young surged into the City box and had his low strike saved by Joe Hart, but the England keeper palmed the ball into the path of Bent, who fired in to mark his high profile transfer with his ninth goal of the season.
That goal was the eighth City had conceded in their last four matches in all competitions, and it spurred them into life as they began to find more of a cutting edge to their attacks.
Vincent Kompany saw a near-post header tipped over the bar by Brad Friedel before former Villa midfielder Gareth Barry glanced an effort just wide of the far post, but still Villa made it to half-time with their lead intact.
City stepped up the pressure after the break, and on the hour mark Mancini swapped Barry for the more attacking Adam Johnson.
Villa had their moments on the break, but the final half an hour was largely spent in the Villa half as City desperately threw all they could at Villa.
A frantic final five minutes saw Nigel de Jong's shot deflect off Ciaran Clark and then off the post, Edin Dzeko head a good chance wide and Kolarov's rasping shot hit Carlos Cuellar when it looked to have beaten Friedel.
In all City had 24 shots on goal, with 14 on target, and 13 corners, but could not find a way through the Claret-and-Blue wall as Villa registered their first clean sheet since October, something as key to them avoiding the drop as the number of goals Bent can score between now and the end of the season.