Bayern Munich came looking for a title party and were served with a cold dose of reality as survival scrappers Mainz earned a stunning 2-1 win over the Bundesliga leaders.
First-half goals from Jonathan Burkardt and Robin Quaison put in-form Mainz in charge, and a leggy Bayern side - who would have been crowned champions with a victory - lacked the zip in their game to overturn that deficit.
Manuel Neuer was at fault for the opener, but also produced some big saves to keep Bayern in touch with their impressive hosts, who have been the most-improved team in the league in the second half of the season.
When Quaison headed the second, he showed the aerial threat that was rarely seen from Bayern's fit-again talisman Robert Lewandowski in this game. Lewandowski snatched a last-gasp consolation after a defensive clanger, but it came too late to be significant.
Burkardt stunned Bayern in the third minute when he was left unattended on the edge of the penalty area and fired a thumping shot that Neuer could only help into the left corner.
Bayern had Lewandowski back in their ranks after a knee injury absence, but before the Polish striker could show any threat they were almost two goals behind, Neuer producing a fine save at full stretch to touch a 20-yard header from Danny Latza against the left post.
Lewandowski fired waywardly from his first chance before Neuer again prevented Bayern slipping two goals behind, Quaison turning Jerome Boateng far too easily and hitting the target with a thumping shot that bounced away off the well-placed goalkeeper.
Bo Svensson's Mainz side, having won four and drawn two of their previous six games to surge out of the relegation zone, doubled their lead in the 37th minute when Quaison headed past Neuer after Philipp Mwene's free-kick from the left proved a perfect, teasing delivery.
Hansi Flick's reaction was to bring on three substitutes at the start of the second half, hauling off Leon Goretzka, who was perhaps fortunate to avoid a first-half red card, plus Kingsley Coman and Leroy Sane, and introducing Eric Maxim Choupo-Moting, Jamal Musiala and Tanguy Nianzou.
A stray arm from Lewandowski caught Mainz midfielder Leandro Barreiro in the face, drawing blood, but it appeared accidental. It was nevertheless not the impact Bayern were looking for from their star striker.
Bayern trailed 2-0 in the first meeting of these sides this season but recovered to win 5-2; however, until Lewandowski's stoppage-time strike, their second-half goal threat in this game was limited to half-chances that the likes of Choupo-Moting and Joshua Kimmich could not convert.
What does it mean? Bayern must re-focus
Bayern must wait for the nine-in-a-row championship celebrations, although surely the champagne will be sprayed before too long. The title will be theirs if RB Leipzig lose to Stuttgart on Sunday, or it may be a matter of waiting until next month. This was a real off day, but Bayern have very few of those and you suspect normal service will soon resume. Mainz, meanwhile, continue to impress. They had lost seven in a row to Bayern before this game, but this Mainz side have become something special and now have 28 points from 16 games under Svensson. Awful in the first half of the campaign, the revival under their new head coach continues apace.
Neuer beaten in number one battle
Bayern would acknowledge that a reliable goalkeeper is the foundation on which successful teams are built, with Oliver Kahn and Neuer having been such pivotal figures for them. Here, on a day when Neuer showed rare fallibility, Mainz's Robin Zentner was supremely solid. He made three saves, two catches and two punches, and in front of him his outfield team-mates thrived. It was cruel that he was left exposed by a poor back-header from Alexander Hack at the death.
Lewy late show but striker looked rusty
Lewandowski had only 10 touches in the first half, lost all eight of his duels, including four in the air, gave away two fouls and looked well off the pace. It was a similar state of affairs after the break too, and perhaps this game came too soon for the striker who has Gerd Muller's Bundesliga goals record in his sights. Given he gobbled up an easy last-gasp chance, though, he might disagree.
Key Opta facts
- Lewandowski is just four goals short of Gerd Müller's Bundesliga record in 1971/72 (40 goals).
- Bayern lost their first Bundesliga away game at Mainz since November 2011 (2-3) after winning the last eight away games against them.
- It was Bayern's fourth Bundesliga defeat this season, with all of them coming in away games.
Bayern are out of the DFB-Pokal so are without a game when the semi-finals take place next weekend. They return to action on May 8 with an Allianz Arena match against Borussia Monchengladbach, while Mainz's next assignment is their May 3 home game against Hertha Berlin.