Technically the sealed bag has to be from an EU airport I think the receipt also has to be sealed in the bag but clearly visible.

Therefore the security could confiscate your spirits, but if the bag is sealed correctly they may not notice (or care) that this was purchased in the US.

It wouldn't make a difference whether you're using flight connections (arriving and going straight through to departures) or doing what you planned to do and go to arrivals lounge first.