Ross Barkley was Chelsea’s lucky FA Cup charm again after Frank Lampard showed his ruthless streak.
Super sub Barkley scored his third goal in this season’s FA Cup run to guide Chelsea into the semi finals as their season goes from strength to strength.
But it came after Lampard made a treble substitution at half-time as he was clearly frustrated with his players after a poor first half display.
And it proved that Lampard is not afraid to make tough decisions and, even though managers have now got five substitutes to choose from, it is still a big call to hook three players after just 45 minutes.
But it reaped rich rewards because on came Barkley together with Cesar Azpilicueta and Mateo Kovacic in place of youngsters Mason Mount, Billy Gilmour and Reece James.
It also showed that, sometimes, there is no substitute for experience as the older heads calmed the nerves, changed the course of the game and, ultimately, it was Barkley who proved to be the match winner.
Barkley has had a strange season, in and out of the team and yet has so much raw power, ability and clearly an eye for goal in this competition having already scored against Nottingham Forest and Liverpool.
Now there will be another chance of silverware for Chelsea and a trophy, plus a place in the Champions League, and that would represent a hugely impressive first season for Lampard at Stamford Bridge.
They have come back well after the restart, winning at Aston Villa, seeing off Manchester City and now a place in the last four of the FA Cup after a very tricky tie at Leicester.
It was frustration for Leicester as, for the third time in the last decade, Chelsea knocked them out at the quarter-final stage.
Leicester boss Brendan Rodgers knows he will have to pick his players up again because the club were desperate for silverware to match their remarkable results in the Premier League and push for a Champions League place.
But they could not make their dominance count in the first half when they were the better team and it was Chelsea who were very sloppy.
Teenage midfielder Gilmour is one of Chelsea’s brightest prospects but was unusually clumsy in possession, James struggled at right back and the visitors were getting a real chasing.
Leicester started brightly with Wilfred Ndidi and Youri Tielemans both forcing Willy Caballero into decent early saves before Jonny Evans glanced a header just wide.
Leicester full back Ben Chilwell was excellent down the left, clearly relishing his audition with Chelsea keen to sign him this summer - and it is easy to see why. Quick, tenacious and good going forward.
But the best chance of the first half fell to Chelsea after 31 minutes after a lovely move. Mount played the ball into Gilmour, his flick set up Christian Pulisic and the in-form winger saw his shot brilliantly pushed over by Leicester keeper Kasper Schmeichel.
However, that was not enough to satisfy Lampard who made running repairs in the drinks break - trying to give Gilmour some encouragement - and made the three changes which is something straight out of the Jose Mourinho brutal school of management.
It will be tough on Gilmour, Mount and James, a blow to their morale but sometimes you have to make tough calls for the good of the team.
Chelsea immediately looked better, looking stronger and in control. The all important goal came after 63 minutes when Willian’s right cross picked out Barkley who timed his run to perfection to sweep the ball into the back of the net.
Leicester pressed and chased a leveller but it was Barkley who came closest to a second goal when he led a late counter attack only to be denied by Schmeichel.
