After the sensational comeback against Paris Saint-Germain, Madrid were euphoric. They had defeated one of Europe's elite, humiliated an economic rival, neutralised Lionel Messi and, many believed, convinced Kylian Mbappe.
They were about to win La Liga and suddenly looked contenders in the Champions League too.
Three weeks later, the advantage in the league is still intact thanks to a scruffy, albeit morale-boosting, win over Celta Vigo on Saturday. But Ancelotti's credit has all-but evaporated.
Real Madrid were waiting to decide if their coach will be able to travel to the first leg of their Champions League quarter-final against Chelsea today, after he tested positive for Covid last week. The outcome of the tie could decide if he continues as coach next season.
It says something about the weight of the Clasico fixture that eight months of largely impressive work can be almost entirely erased by one, disastrous, 90 minutes.