- Xabi Alonso's side have taken 31 points from a possible 33 this season.
- Leverkusen have won 16 of their 17 matches in all competitions this season, including the past 12 in a row.
Bayer Leverkusen returned to the top of the Bundesliga with a 4-0 home win over Union Berlin.
Xabi Alonso's side have taken 31 points from a possible 33 this season, equalling the record set by Pep Guardiola's Bayern Munich in 2015-16.
Alex Grimaldo, Odilon Kossounou, Jonathan Tah and Nathan Tella scored as Leverkusen replaced Bayern at the top.
"The feeling is great at the moment," said former Spain and Liverpool midfielder Alonso.
"We have played with a lot of focus and concentration. But there are still a lot of matches and a lot can happen in football and suddenly all expectations are gone."
Leverkusen have won 16 of their 17 matches in all competitions this season, including the past 12 in a row.
Alonso was appointed in October last year with Leverkusen second from the bottom of the table after eight games.
They ended the season in sixth and reached the Europa League semi-finals.
Alonso's only previous managerial experience was three years in charge of Real Sociedad's B team, having retired from playing in 2017.
Champions Bayern moved to the top of the table with a 4-2 win over Heidenheim on Saturday.
Union Berlin stays bottom on goal difference following a club record ninth successive defeat.