I also guessed the same, Real Madrid has better stats for the previous matches. But it is a home match for Atletico Madrid, they always have good motivation to win at home. So, it is not very surprising if they can play more aggressively today, especially in the first half of the match. Atletico players know well how to take advantage from the poor starting line up of Real Madrid.
FYI, final score is Atletico Madrid 3-1 Real Madrid.
Real Madrid just conceded their first defeat in the league after maintaining 5 matches unbeaten, I feel so sorry for the Madrid fans that viewed the match with hopes of winning the game because everyone taught Atletico Madrid were not in a very good form to face Realmadrid and they would easily beat them but the difference became the case and Madrid were only able to score a consolation goal.
If you check the Stats you'll see that Realmadrid's were very dominant in the match and had better chances of winning the game they had about 20 shots with 5 on target and played about 11 corner more than that of Atletico Madrid, they didn't have a very finisher and Jude Bellingham was unlucky to rescue them today, Realmadrid needs to start looking for another striker against the upcoming winter windows cause they can't be depending only on Jude Bellingham always, and Joselu is not who they can fully rely on.