Real Madrid didn't lose, they just failed to win a match they should have won. However I have to admit that Sevilla played well in that match even though they deserved to lose points at home if not for two disallowed goals, but that is another part that should not be the reason why Real Madrid didn't win.
Sevilla is certainly very confident of performing well at home, and this is proof that they are really able to get into good form after sacking their old coach. Playing a draw against Real Madrid is the same as winning the match, but this draw has certainly harmed Real Madrid, who are in fact the favorites. Sevilla didn't score any goals apart from Alaba's own goal, but they fired 17 shots, 7 of which were on target.
Yeah Madrid failed to win a game everyone considered they would win without much stress but they couldn't survive the defense by their ex team mate Ramos who was very outstanding in yesterday's game. Real Madrid though at the top of the table at the moment, they are not safe enough as they needed that goal difference to keep them strong at the top but they currently lack that difference.
If Barcelona happens to win their game today by two ore more goals they will top Madrid by The goal difference as they are only three points away from Madrid, but if Madrid had won it would have been five points difference, but if Barcelona draw Madrid may be most likely safe at the top of the table till next weekend, more was expected of Madrid, they had a complete squad on the pitch so it was expected they did better.