Chelsea 5 Leicester City 2
Gary Cahill and Salomon Kalou put the hosts ahead in the first-half, before Torres scored from close range after the break - his first goal in 23 hours of football.
Jermaine Beckford pulled a goal back for the Championship side although Torres' near post header restored Chelsea's two-goal advantage.
Ben Marshall's sublime effort from 30 yards gave Leicester a lifeline, but Raul Meireles' injury-time strike ended any chance of a memorable comeback.
Chelsea were good value for their 5-2 win and created a number of scoring opportunities, although Leicester manager Nigel Pearson will be unhappy with how some of some of the goals conceded.
As expected, the first-half was one-way traffic, with only a crucial block from Wes Morgan preventing Fernando Torres from getting on the score sheet within the opening few minutes of the match.
Torres would cause the Leicester backline problems all afternoon, Sol Bamba on the receiving end this time as he allowed the Spanish international to cut inside him into the penalty area as Wes Morgan was forced to clear the ball behind goal.
The ensuing corner-kick by Juan Mata was headed home from six yards by an unmarked Gary Cahill, who unveiled a 'Praying for Muamba' t-shirt, a mark of respect to his former Bolton Wanderers team-mate Fabrice Muamba, who remains in a critical condition after collapsing on the pitch against Tottenham Hotspur yesterday afternoon.
Chelsea, high on confidence after an impressive 4-1 midweek win over Napoli in the Champions League, came close to doubling their lead moments later after excellent footwork from Daniel Sturridge allowed Raul Meireles to shoot from close range, and although his strike beat Leicester goalkeeper Kasper Schmeichel, full-back Paul Konchesky was on hand to clear the ball off the line.
Leicester, who already looked on the ropes, found themselves 2-0 down after seventeen minutes when Fernando Torres raced down the flank before squaring to Salomon Kalou, who initially struggled to get the ball out from under his feet but regained his composure to finish coolly into the bottom corner.
The goal came from excellent work by Torres, who looked more like the prolific front man Chelsea fans had expected, rather than the striker who had previously netted just six times since his switch from Liverpool in 2011.
At the other end, Paul Gallagher fired over from distance before Sturridge struck just wide after getting the better of Sol Bamba again.
Fernando Torres then tested Kasper Schmeichel with a couple of shots from long range, in what would turn out to be a long day for the Danish goalkeeper, but he was equal to both strikes this time around.
Lloyd Dyer then set up Richie Wellens after a rare first-half attack by Leicester, but the Foxes captain dragged his shot wide of Peter Cech's goal.
Chelsea were dominating the midfield battle but Leicester's Neil Danns was still in fine attacking form, forcing Cech into a near-post fingertip save ten minutes before the break.
Leicester, to their credit, kept searching for a way into the match and might have done so through Lloyd Dyer after good work from Paul Konchesky and David Nugent, but the speedy winger pulled his shot over the bar as the first-half came to a close.
Substitute Florent Malouda was the first to try and extend Chelsea's lead in the second-half, but his shot flew wide after Leicester's defence continued to let attacking players cut inside.
Just before the hour mark, Sol Bamba was on hand to cut out Fernando Torres' pass to Daniel Sturridge in what would have been 3-0, although Chelsea did get their third shortly afterwards when Raul Meireles got the better of the struggling Bamba before the ball ended up at the feet of Torres, whose scuffed shot found its way past Kasper Schmeichel.
It was a long overdue goal for Torres and, although it came against lower league opposition, will be one both he and his team-mates remember as the one that ended his 152-day goal drought.
Torres could have scored again moments later as Chelsea continued to hammer the crumbling Leicester defence on the counter-attack, but his more spectacular strike flew just over the crossbar.
The visitors were handed a lifeline with thirteen minutes remaining when Neil Danns' thunderous strike from 25 yards smashed against the post, the rebound falling into the path of Jermaine Beckford who was on hand to tap home past the helpless Peter Cech.
It was Beckford's fifteenth FA Cup goal in as many starts, and a deserved one for Leicester who had continued to attack Chelsea in the second-half despite finding themselves at a disadvantage in terms of both pace and class.
Torres did restore Chelsea's three-goal cushion with five minutes remaining after poor marking from a corner-kick allowed him to ghost in at the near post to head across goal and past a helpless Kasper Schmeichel, although Ben Marshall's emphatic 30-yard curling strike made it 4-2 just minutes after the restart gave the travelling 6,000 Leicester fans something to cheer about.
Raul Meireles put the Blues three goals ahead once again, with Torres again involved, this time the Spaniard racing down the left wing before picking out the Portuguese midfielder who coolly finished past Schmeichel from fourteen yards.
The final whistle ended Leicester City's FA Cup dream, but gave a resurgent Chelsea side a very realistic chance of winning some silverware this year after a difficult season.
Man of the Match - Fernando Torres