Pellegrini got it wrong at the start
A muscle injury to Fernandinho suffered in training meant that Pellegrini had to start one of his most important matches, without a player who has grown in importance as the season has wore on. And whilst that was a blow, the litany of stars at his disposal meant that he could have chosen any one of Jack Rodwell or James Milner.
Instead, the Chilean went for a 33-year-old center half, who has looked far from convincing this far to stifle Hazard.
In the 31st minute, the center back misjudged a ball played to Hazard, allowed him move infield, pass it to Ramires and let Branislav Ivanovic open the scoring.
At the top, where there is so little margin for error, Pellegrini had made a big mistake, in not just starting with Demichelis, but also persisting with him in the second half, when all evidence pointed towards showing him the door.