Atalanta for a truth aren't as Liverpool but for a club that's been tearing teams apart this season and currently at the top of the Italian Serie A table, it's very possible that they can beat Real Madrid at home.
That said, I'm a passionate Real Madrid fan who believes so much on the strength and experience of the team so I'm optimistic that Carlo Ancelotti's men will win at Atalanta but that's of they'll play at their best
Sure, Atalanta isn't as strong as Liverpool. But Atalanta is possible to beat Real Madrid. Atalanta have defeated some big teams this season, they could defeat a team like Napoli, Roma, and AC Milan. Even if Atalanta defeated those strong teams in domestic competitions, it can reflect the strength of Atalanta this season. However, Atalanta isn't a team that has a very good record playing at their home. So, it makes sense if you assume Real Madrid still can beat them and get 3 points. Moreover if Real Madrid played with their best players. Real Madrid squad quality looks a much better than Atalanta squad quality.