The 50 million-pound Spanish striker scuffed a shot into the net after 67 minutes and he struck again with a deft late header as Chelsea's revival continued under caretaker manager Roberto Di Matteo.
"I needed those goals, in the last month the team is much better than before," man-of-the-match Torres told ESPN. "I have been playing well but not scoring goals. We are creating more chances than before and we are much better defensively."
Defender Gary Cahill headed Chelsea's first goal before revealing a T-shirt with "Pray for Muamba" written on it, a reference to his former Bolton Wanderers team-mate Fabrice Muamba who collapsed during the FA Cup tie against Tottenham Hotspur on Saturday and remains critically ill in hospital.
Torres set up the second for Salomon Kalou to put Chelsea firmly in control and the Spaniard's first goal in 25 matches effectively sent the London club into the last four before the match ended in a flurry of action.
Leicester pulled one back through Jermaine Beckford, Torres neatly glanced in a corner, Ben Marshall's superb 25-metre shot flew past Chelsea goalkeeper Petr Cech and Torres set up his side's fifth for Raul Meireles in stoppage time.
"The whole club, the team and the supporters were happy. He works hard and you get rewarded when you work hard in life," Di Matteo told reporters.
"Hopefully his confidence is going to be very, very high now... not only is he a very good player but he's a good guy as well.
"We've overcome every hurdle so far. I haven't had time to enjoy it because the games are coming so fast."
SUBLIME FINISH
Liverpool opened the scoring against Stoke at Anfield after 23 minutes thanks to a sublime finish from Luis Suarez, the Uruguayan striker stroking the ball into the corner of the net from 20 metres.
Last season's FA Cup runners-up struck back quickly, however, former Liverpool forward Peter Crouch nodding in the equaliser following the award of a controversial corner to the away team.
Liverpool, who won the League Cup last month, dominated possession after half-time and they got their reward after 57 minutes when winger Stewart Downing ran across two Stoke defenders in the penalty area before drilling a firm shot past goalkeeper Thomas Sorensen.
"Stoke are a tough physical side and Tony Pulis had them wound up because it was very big game for both sides today," Liverpool captain Steven Gerrard said.
"It was even-stevens in the first half but in the second half we took over and controlled the game. Stewie took his goal fantastically well and off we go to Wembley again."
Everton drew 1-1 with Sunderland on Saturday and the game between Tottenham and Bolton was abandoned before half-time with the score at 1-1 after Muamba collapsed on the pitch.
Chelsea will play Spurs or Bolton in one semi-final at Wembley and Liverpool face the winners of the Sunderland
