Torres returned from injury to fire his side in front with a Kop end goal midway through the second half. Substitute Ngog then wrapped up the points with almost the last kick of the game.
 
A second yellow card with minutes to spare for Nemanja Vidic piled more misery on United, for whom former Liverpool star Michael Owen featured as a substitute.
 
The only sour note for the Reds was the dismissal of Javier Mascherano, who received a second yellow in stoppage time for a foul on Edwin van der Sar.
 
The result leaves Liverpool just six points behind new league leaders Chelsea, and just as importantly lifts the mood around Anfield after a difficult month.
 
For the second season running Liverpool went into this fixture without injured skipper Steven Gerrard in the starting line-up, but Benitez could at least call upon Glen Johnson and Torres on his 200th league game in charge after both passed late fitness tests.
 
With two of the big guns back, it took Liverpool just five minutes to carve their way through United's defence when Dirk Kuyt and Yossi Benayoun combined superbly to tee up Lucas on the edge of the box. The Brazilian's shot was deflected wide for a corner but it augured well for a Reds side supposedly low on confidence.
 
The Kop were in good form too, pelting beach balls on to the turf before kick off in an ironic nod to the freak goal which cost their side so dearly in Sunderland a week ago. It takes more than Liverpool's worst run of defeats for 22 years to dim the Scouse sense of humour.
 
The mood around Anfield was almost lifted further on 15 minutes when Torres was hauled down by Patrice Evra. Fabio Aurelio stepped up to try and repeat his set-piece goal at Old Trafford in March but this time he was thwarted by a fine save from van der Sar. First Kuyt and then Torres pounced on the parry but United escaped.
 
Minutes later Lucas ran beyond the visiting midfield before playing Kuyt through on goal, but the Holland international dragged wide.
 
United didn't have a sniff until 20 minutes when Wayne Rooney and Dimitar Berbatov orchestrated a move which sent Antonio Valencia into space down the right. Rooney connected with the resulting cross but the save was comfortable for Pepe Reina.
 
A stunning tackle from Jamie Carragher stopped Michael Carrick in his tracks when United next threatened, but it was Liverpool who had by far the better of the first half.
 
Arguably their best chance came 10 minutes before the break when Benayoun crossed over the heads of Rio Ferdinand and Vidic only for Aurelio to nod a free header straight at van der Sar.
 
The second half began in a similar fashion when Benayoun teased United's central defenders before laying to Kuyt. The Kop begged for a shot but instead the Dutchman squared back to Benayoun, who by now was surrounded and unable to get a shot away.
 
Next Torres evaded the offside trap down United's left but elected to cross rather than his trademark cut inside. No one was there and the scores remained level.
 
Liverpool were defending superbly and attacking with force. Carragher was back to his best, while nothing seemed to be getting past Mascherano in midfield. The Argentina captain was even playing his part going forward, knocking Rio Ferdinand flat with a piledriver from 30 yards.
 
The opener, then, was fully deserved when it arrived on 65 minutes. Benayoun supplied the pass for Torres, who shrugged off Ferdinand's foul before blasting beyond van der Sar and sending the Kop wild.
 
It could have been 2-0 on 71 minutes when Lucas thundered a left-foot effort high into the stands from a corner. The crowd almost missed it, so busy were they offering Owen a feisty reception during his first foray down the touchline to warm-up.
 
United's injury-plagued free transfer was introduced on 74 minutes looking to break his goalless record against the club that made him.
 
Valencia tried to show Owen the way after finding himself in space 10 yards out but fired too close to Reina.
 
United were pressing for an equaliser but Liverpool looked dangerous on the counter, and Benayoun could have doubled their advantage after skipping past Evra only for Vidic to make a crucial interception.
 
Valencia hit the bar from close range on 84 minutes but it was as close as the visitors came.
 
The day ended in drama as both sides were reduced to 10 men. First Vidic went for a cynical foul on Kuyt, then Mascherano was dismissed for a late challenge on van der Sar.
 
The points were then sealed by David Ngog deep into injury-time after the French ace evaded the linesman's flag and slotted past the goalkeeper.