As the league leaders fell at home to West Ham, they did not only concede their first goal of the season, but they showed their first signs of fragility (at least at domestic level). Backs-to-the-wall doesn’t quite explain the extent to which West Ham defended in the second half, with one of the best rear-guard displays you will ever see.

Whether it was Sergio Aguero, Kevin de Bruyne or Yaya Toure, Hammers bodies flew in front of every shot going towards their goal and produced one of the bigger upsets of the season.

Diafra Sakho was excellent on the break and the West Ham defence put in one of the performances of their lives.

Here are three things we learnt from the day:

Kevin de Bruyne is the real deal (in case you didn't know)

The ex-Chelsea man is, inevitably, under a great deal of pressure since his big money move from Wolfsburg but he has already shown his class.

Playing at number 10, rather than wide right if Silva was fit, De Bruyne’s passing was as accurate as anyone could dream of and his goal just capped a very complete performance. Although he was ostracised at Chelsea, De Bruyne is certainly the real deal and a genuine coup for City.

Slaven Bilic is utterly fearless

Most managers, including those at big clubs, would go to the Etihad ready to walk away with a point and sit back.

Despite the second half onslaught, West Ham never showed a ‘bus parking’ attitude and continued to show forward momentum throughout. In the dying embers of the game, Bilic pushed his men to keep City in their half and even his starting line-up reflected his ambition. Partly due to injury, Bilic did not opt for the three man midfield he took to Anfield, but played an expansive game looking to attack a centre-back partnership in their first start together.

Bigger clubs should have moved for Winston Reid

With the opportunity to snap up the Kiwi centre-back last summer, it is remarkable that no big club made a move for the West Ham man.

Another big game performance from Reid makes him my man of the match and, with so many sides struggling defensively, it is bizarre that none of the ‘bigger’ sides made a move for this New Zealander.

His willingness to throw his body on the line and lead his backline puts him up there with the very best defenders in the league.