Ramires tumbled under challenge from Evra while Torres went down as he tangled with Antonio Valencia.
Ramires scored for Chelsea in the 46th and 69th minutes around James Milner's goal for City in the 55th.
Elano sought to change that trend with a back-post cross that was headed high over the top by Chelsea's Ramires.
Chelsea paid a huge price for Ramires' generosity as United struck twice before half-time to put themselves firmly in control.
Ramires was later booked and will miss the match against the Dutch.
The attacking trio of Oscar, Neymar and Hulk provided a real threat, while Ramires and Paulinho had recently shone in the center of midfield.
Benfica's two wide men, Di Maria and the Brazilian youngster Ramires, carved out an early opportunity for Saviola, but he had strayed narrowly off-side.
They came out in inspired form at the start of the second half and Oscar picked out fellow Brazilian Ramires to head the equalizer.
Ramires also shot wide and an away goal seemed inevitable but Wolves were awoken from their slumbers by a very clumsy studs-up challenge by Lampard.
Lampard remained an unused substitute but Chelsea's win more than justified Villas-Boas's decision to hand midfield responsibility to Ramires, Raul Meireles and impressive youngster Oriol Romeu.
Fernando Torres was wasteful as Chelsea dominated, the Spaniard's touch letting him down when put through by Luiz and then nodding over a cross by Ramires.
But Chelsea wasted chances to wrap up the match, Ramires missing from close range and Fernando Torres firing agonizingly wide to leave Benfica with late hope.
When they did produce a threat, Ramires had a shot easily saved while the forward's control let him down when Kaka tried to put him through.
Torres scuffed an angled finish after Anderson carelessly conceded possession and another culprit was Ramires, who was guilty of an awful miss in the 25th minute.
Ramires had the first chance for Brazil, but fired against the outside of the post from a tight angle having been played in by the lively Fabiano.
Ramires did well to win possession before feeding Cole, whose near-post cross was met with a subtle flick from Drogba that flew in via the near post.
Ramires hit the home side's post with a shot late on, while Nicolas Anelka was denied by Tim Howard and Jack Rodwell had an effort saved by Cech.
Alves came on late in the game and powered a strike into the far corner after Aaron Mokoena had conceded the set piece with a foul on Ramires.
Daniel Sturridge then gave Chelsea the lead for the first time in the contest on 97 minutes and Ramires made sure of the victory added a fifth late on.
And the comeback was complete when Chelsea swept down field after a United attack and Ramires cut inside his man to beat De Gea with a precise left-footed finish.
Drogba was trying manfully to spark life into Chelsea and he fashioned a chance for Ramires that the Brazilian, arriving at pace in the area, could only divert wide of the target.
The impressive Juan Mata played in Torres, who unselfishly squared the ball for Ramires in front of an open goal, but his weak finish allowed De Gea to make a scrambling save.
Torres continued to have chances after the interval and, again, he was wasteful as the 26-year-old rose well to nod over a dangerous cross from Ramires, before curling over from the left minutes later.
Only a last-ditch tackle from Michel Salgado denied Didier Drogba after a clever through-ball from Anelka and, from the resulting corner, Ivanovic flicked the ball on for Ramires, who lashed a half-volley against the bar.
They'll play without several of their top players, losing Terry, Ramires and Branislav Ivanovic to forced suspensions, but after bringing down the game's ruling power, Chelsea just might have one more improbable win in them.
The hosts were by now on top and, after Drogba had fizzed a shot over from 30 yards, they were furious when Ramires was cautioned for diving following a challenge by Howard in the penalty area.
Chelsea went in front after just six minutes as Mata controlled and finished precisely past Wojciech Szczesny from Cesar Azpilicueta's pass, with Arsenal claiming a foul from Brazilian midfielder Ramires on Francis Coquelin in the build-up.
Even with Benitez's decision to rest the likes of Eden Hazard, Ashley Cole, Ramires and Juan Mata, Chelsea was expected to see off a QPR side which had already lost 12 of its 20 league games.
应用推荐