It is impossible to keep the unbeaten record, Leverkusen already experienced a lose in the match against Leipzig. I am quite surprised that Leverkusen got a first defeat in their home. I think they will get a draw or win against Leipzig. They really dominated the match, unfortunately they only scored 2 goals. I think they are just unlucky in the match, they have done their best.
However, it is true that they are still possible to win the title. It is still in the early of the season, there are many chances to get points. But I think it is time for Xabi Alonso to evaluate the tactics. He should focus on the attacking only, he must be more aware about the defense. I think Leverkusen defense is decreasing a lot, Xabi should wisely choose the best defenders and goalkeeper in every match. I don't know why he choose Kovar over Hrádecký in the match against Leipzig.
This is not a big surprise, Leipzig is a strong team and Leverkusen was also unlucky in that match so it is natural that they lost.
But overall Leverkusen has shown good performance, so I think the defeat does not need to be exaggerated, Leverkusen is still a strong team like last season.
Xabi Alonso has proven that he is successful enough to be able to lift Leverkusen's performance, so from their defeat at the beginning of this season there is no doubt that there will be a decline in performance, in fact I think that Leverkusen's defeat is because Leipzig has improved its performance so that it is likely that there will be fierce competition in the Bundesliga this season with several teams competing fiercely for the title.