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."
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.
"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."
