The Spaniard scored his first goals since his double against Genk in the Champions League group stage on October 19 as the Blues dominated their Championship rivals to book a ticket to Wembley for the semi-finals.
Gary Cahill opened the scoring for Roberto Di Matteo's side in the 12th minute with a front post header from Juan Mata's corner for his first goal for the club and he celebrated by revealing an undershirt which read 'Pray 4 Muamba' in reference to his former Bolton teammate Fabrice Muamba who collapsed yesterday under cardiac arrest.
Chelsea's lead was quickly doubled when Torres played a neat ball into the path of Salomon Kalou who took a touch, settled, and then slotted past Kasper Schmeichel for his first club goal since early December.
The Blues' two-goal lead then became three in the 67th minute when Torres broke his five-month and 1,541-minute drought with a scuffed finish from Raul Meireles cut-back from the right side of the area lifting an enormous weight from the shoulders of the former Liverpool ace.
With 12 minutes remaining, Leicester managed to get one back when Jermaine Beckford netted his 15th FA Cup goal in 18 appearances with a close range finish after Neil Danns' swerving shot had cannoned back off the upright but the Foxes' joy was short-lived as Torres helped himself to a second.
This time he headed home Meireles' corner at the front post to make it 4-1 before Ben Marshall added a second for the visitors with a sublime goal after he ran at the Chelsea defence and unleashed an unstoppable curler past Petr Cech.
But the goalscoring had not finished there as Meireles capped off a great performance with a neat finish from a Torres pass from about eight yards to make it 5-2 as the Blues won their fourth in a row under Di Matteo.
FA Cup quarter-final
Stamford Bridge, London - 38,276