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When Chelsea chose to let Frank Lampard leave in the summer, there was always a fear that the decision could come back to haunt them.
Both sides claimed the choice came from the other, yet at 36-years-old, the midfielder was deemed past his best.
For 13 years, Lampard had made a speciality of arriving late into the box in a blue shirt and firing past bewildered keepers.
He did it on a club record 211 occasions, yet here he was at the Etihad Stadium striking a painful blow in the lighter shade of blue.
For having agreed a move to MLS side New York City and vowing never to play for another Premier League club, Lampard agreed a six-month loan spell at Chelsea's main title rivals.
This was only his second appearance for his new club and he came on the pitch with just 12 minutes remaining. His new club were 1-0 down and in dire trouble.
There were more than three points at stake here. Chelsea had taken the lead through Andre Schurrle and were heading to an eight point lead over them in the table.
Chelsea should have had a second consecutive League win here in the bag. But for Diego Costa striking a post, they may have done.
However, their defence which has been letting them down all season and did so again here.
These players know the way Lampard operates more than anyone. Yet first Andre Schurrle was guilty of switching off to allow James Milner to run in behind him.
But even worse was Branislav Ivanovic. He was right with Lampard but let him run unmarked into the area to convert Milner's cross and get Manuel Pellegrini out of jail.
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The Chelsea fans who had sang his name throughout most of the encounter were silenced. Now it was the City fans heralding their hero and taking great delight in mocking the club who allowed him to go in the first place.
Manchester City will argue that justice was done. They were the more adventurous team throughout and barely gave the League's top scorer, Costa, a kick.
The physical contest always threatened to see a red card as referee Mike Dean started to bring his yellow out regularly.
In the end Pablo Zabaleta was the victim. The right back had been punished for hacking down Eden Hazard in the first half and then was shown a second for an altercation with Costa in the second.
With some space to finally play into, Chelsea capitalised to take the lead with their only decent move of the match. Hazard squaring the ball to substitute Andre Schurrle to tap home from close range.
Chelsea looked set to be sitting pretty at the top, only for Lampard to punish their porous defence, which has kept just one clean sheet all season.
The Blues remain fight points clear of the defending champions, but they will return to the capital knowing they let a golden opportunity as well as their greatest-ever midfielder slip from their fingers.
