Sunday's 5-0 victory over Werder Bremen ended a trophy drought of 31 years since a German Cup success in 1993, five years after they lifted the UEFA Cup.

They erased a Bayern Munich record by extending their impressive unbeaten run all season to 29 Bundesliga matches, and with five games left have the chance to become the first German top-flight team to not taste defeat in a full campaign.

Unbeaten in 43 matches in all competitions, Leverkusen can claim a treble as they are big favourites in the German Cup final on May 25 against second division Kaiserslautern and they're still in the Europa League.

"Football history owes Bayer Leverkusen a Bundesliga title," former player and long-time club official Rudi Voller said.

A series of near misses in the past earned the club owned by pharmaceutical company Bayer the nickname of Vizekusen, or Neverkusen in the English-speaking world.

The club had the name Vizekusen protected by the national patent and brand office until 2030, with former managing director Wolfgang Holzhauser explaining this was not for self-mockery reasons but to deny others from making a profit using the name.

A Bundesliga title seemed far away four years ago, and they found themselves in the danger zone early in 2022-23, prompting the exit of Gerardo Seoane and appointment of Alonso.

Alonso, 42, had never coached a first team before as he arrived from Real Sociedad's reserves but he had a winning mentality as a player - having lifted the World Cup and two Euros with Spain, the Champions League with Real Madrid and Liverpool, and national titles with Real and Bayern Munich.

And just like he helped Liverpool win the epic 2005 Champions League final from 3-0 down against AC Milan, he led a Leverkusen turnaround from the relegation zone to sixth place and the Europa League semis.

They ended last season with a 3-0 defeat in Bochum on May 27 and have not tasted defeat since then in a more remarkable run this term.

But they were cautious about celebrating too early.

Leverkusen lost three Cup finals and had five Bundesliga runner-up finishes, including in 2000, when an own goal from star midfielder Michael Ballack meant they lost at Unterhaching on the final day to gift Bayern the trophy.

Two years later, Leverkusen blew a five-point league lead in the last three matches, with Borussia Dortmund finishing top, and over the next 11 days also lost the German Cup and Champions League finals against Schalke and Real Madrid respectively.

Not this time, though. Never say Neverkusen again.

Australian Associated Press