The stats tell the story.
The 2-0 defeat at Etihad Stadium will be a big disappointment for Jose Mourinho and his players. After all, it now leaves them with the Premier League and Champions League as their only hope of silverware in 2013-14 and by Mourinho's own admission, this team is not yet ready to scale such heady heights.
Indeed, while the Blues have been turning on the style this season, Mourinho has endeavored to steady expectations. After every impressive performance he has rolled out the same line that his team isn't quite the finished article. "We're just a little horse," has been the soundbite, as per the BBC.
On the back of a sobering week at Stamford Bridge, perhaps he is right.
Chelsea threw away a one-goal lead against relegation-threatened West Bromwich Albion on Tuesday, drawing 1-1 at The Hawthorns. Results elsewhere—and City's game with Sunderland being postponed—meant they remained top of the table, but to drop out of the FA Cup the way they did on Saturday reminds us they are far from invincible.
Mourinho outwitted Manuel Pellegrini when these sides met in the Premier League just under two weeks ago. That night Mourinho's Chelsea controlled the game, stifled City tactically and came away from the Etihad with a well-deserved three points after Branislav Ivanovic's first-half goal proved enough to separate the sides.
Not this time. Pellegrini learned his lesson and City did a complete reverse, bossing Chelsea in much the same way as the Blues had done to them 12 days previous.
Chelsea had little answer to the energy the home side showed, suffocating space and giving the likes of Eden Hazard and Willian little joy in possession as a result.
Whereas that duo was so influential before, their impact this time out was nonexistent.
Even in the middle of the park, where Nemanja Matic had previously won his personal duel with Yaya Toure, Chelsea were overrun this time and had little to offer in response.
"Today proved how difficult it is to win here [at the Etihad], which shows how well the team did in the last game," was Mourinho's summary of events, as per the official Chelsea Twitter feed.
There is a habit in the modern era for one loss to be blown out of proportion. Losing to City doesn't change much in terms of the Blues' title aspirations, so when they return to league duties to face Everton on Feb. 22, it will be business as usual. Chelsea will be top and it will be down to the rest of their rivals to catch them.
The bigger picture tells us a lot more, however.
Whereas points have been dropped to inferior teams this term, coming in games where Chelsea could claim to be unfortunate and blame their own errors on defeat, it was different against City.
The Blues came up against a better team and were totally outclassed. It's among the few times it has happened since Mourinho's return and highlights the point he has been eager to raise at every opportunity—that his team is still learning.
In contrast, Pellegrini's side had the look of a team ready to achieve something, whereas the Blues appeared starved of leadership and lacked the nous to negotiate a major cup tie.
There are going to be plenty of battles between now and the end of the season. Chelsea came out on top in a significant one at the Etihad Feb. 3, but the bragging rights are now City's and as a result, Pellegrini's men look far more equipped to win the war.
Garry Hayes is Bleacher Report's lead Chelsea correspondent and will be following the club from a London base throughout the 2013-14 season. Follow him on Twitter here @garryhayes
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