Germany's top two clubs go head to head on Saturday with hosts Borussia Dortmund out to ignite the Bundesliga title race by further trimming the lead of Pep Guardiola's Bayern Munich.

Bayern seemed to be running away with a fourth straight league title, and enjoyed an eight-point lead over second-placed Dortmund, until Mainz slammed on the brakes with a shock 2-1 win at the Allianz Arena on Wednesday.

It was only Bayern's second league defeat of the season.

Dortmund's 2-0 win at Darmstadt the same night meant Bayern's lead was cut to five points and adds spice to an already mouth-watering clash at Borussia's Signal Iduna Park, but the Bavarians remain favourites.

When the sides met last October, Bayern dealt Dortmund a 5-1 thrashing in Munich.

Bayern have won four of the last five league meetings including victories in both of their last two visits to Dortmund.

Dortmund's single Bundesliga victory over Bayern in the last four years was a 3-0 thumping in Munich in April 2014 when Guardiola's side had already won the league title with a record seven games to spare.

But for the first time in his three seasons at Bayern, Guardiola has a league rival breathing down his neck.

"This Borussia Dortmund team is completely different to the last three years," said the Spaniard after losing to Mainz.

"We will have to fight until the last game and the last second."

The Dortmund camp has sniffed weakness in their rivals.

"Let's not beat about the bush -- we want to cut the gap to two points," said Dortmund captain Mats Hummels.

"Saturday's going to be a brilliant game, we'll be really up for it."

Guardiola has a longer injury list than Dortmund coach Thomas Tuchel, who is only missing centre-back Sokratis from his first-choice line-up.

Injuries to Jerome Boateng, Javi Martinez and Holger Badstuber have forced Guardiola to convert left-back David Alaba into a centre-back alongside Mehdi Benatia.

But Guardiola has an embarrassment of riches in midfield with Franck Ribery back from injury and Germany's World Cup winner Mario Goetze unable to get a game.

Whether he plays or not, Goetze, like fellow ex-Borussia star Robert Lewandowski, can expect a another hostile reception from home fans on his return to Dortmund.

A sub-plot to the showdown sees the league's top three scorers shooting it out in Dortmund.

Bayern's Lewandowski tops the list with 23 goals in his 23 games while Dortmund's Pierre-Emerick Aubameyang is just one behind with 22.

Munich's Thomas Mueller has also scored a highly respectable 17 league goals. Between them, Mueller and Lewandowski have 40 league goals.

They are just 14 short of the league record partnership of 54 set by Wolfsburg pair Edin Dzeko and Grafite in 2009.

"You sometimes get games (like the Mainz defeat), but it will be different in Dortmund," promised Lewandowski ominously.

There will be a relegation battle royale when Werder Bremen, who stunned Bayer Leverkusen 4-1 on Wednesday thanks to veteran Claudio Pizarro's hat-trick, host bottom side Hanover 96.

Bremen remain just one place above the bottom three while Hanover, who have playmaker Hiroshi Kiyotake back from injury, are seven points from safety and desperately need to win.

Second-bottom Hoffenheim will be looking to build on their 2-1 win over Augsburg when they travel to Stuttgart, who are winless in their last three games after a surge which carried them up to mid-table.

Fixtures (all times 1430 GMT unless stated)