City have made smooth progress through the rounds to reach the last four.
Roberto Mancini's side has scored 13 goals and not conceded any.
Rafa Benitez's team raised its game to come through two ties with Manchester United to reach the last four and to get within touching distance of their fifth FA Cup final in seven seasons.
The two clash on April 14 at Wembley, and here are a few predictions for what's sure to be a good matchup.
With a serious challenge for the Premier League title the priority for both clubs this season, it's no wonder they have mixed up their sides for the cup competitions.
The landscape now, though, is very different.
Cups are the only things Chelsea and City can win, and they will both be going all out for victory.
No more Pantilimon, Kolorov, Nasri or Sinclair.
No more Bertrand, Mikel, Oscar or Moses, nor Torres for that matter.
Both managers know their jobs are on the line.
In Benitez's case, he's fully aware his time is up and will use the last few weeks of the season as an exercise in trying to pad-out his resume.
Even if City win their derby with Manchester United before the semi-final, they'll know the FA Cup is still the main focus.
Frank Lampard needs three goals to become Chelsea's greatest-ever goalscorer.
He currently has 200 and firmly has Bobby Tambling's mark in his sights.
With three games to play before the semi-final, there's an outside chance he could break it before he steps out at Wembley against City.
However, there would be no better place than the national stadium to do it for Lampard, who is still set to leave Chelsea at the end of the season.
Would a new record be enough to change Chelsea's mind?
The pressure of semi-finals can get to you.
Teams are playing at their maximum and on the edge.
Margins for error are minuscule.
This season both Chelsea and Manchester City have had commendable records when it comes to counting up the fouls.
City are 13th in the foul league with 31 offences.
Chelsea fare even better with 23, the lowest in the division.
City have three red cards and Chelsea, two.
The last time these sides met at Wembley in the Community Shield at the start of the season there were eight yellows cards and Branislav Ivanovic was sent off.
With the stakes even higher this time round, expect someone to walk again.
Statistics courtesy of Whoscored.com.
Although the wrath of Wigan and Blackburn fans is being risked, the winners of the semi-final between Chelsea and Manchester City will go on to lift the FA Cup in the final.
Upsets can and do happen, of course, and we all remember Sunderland, West Ham and Wimbledon doing just that over the years.
But that's not going to happen this year.
Chelsea and City will see their meeting in the last four like it's a final.
They will put everything on the line knowing that Premier League strugglers Wigan or Championship crisis-club Blackburn should be beatable in the showpiece on May 11.
That's why their semi-final should be a belter.
If there's one player who is due to hit form it's Manchester City's Sergio Aguero.
The Argentina master wrote himself into City folklore when he scored the goal that clinched the Premier League title in such dramatic fashion last May.
This time around he has not had such a good time.
His 13 goals withers in comparison to the 30 he scored in 2011-12.
Aguero's form has been affected by injury, but he is now back in contention and who would back against him digging City out of a hole on May 11?
The semi-final with Chelsea will be City's biggest game of the season, and noone has a better big-game reputation than Aguero.
He will be the match-winner.