Bayern stunned as Mainz gives Dortmund a lift
Bayern Munich's troubling start to Thomas Tuchel's reign continued as the champion slumped to a 3-1 defeat to Mainz at Mewa Arena to surrender the Bundesliga lead.
Die Roten looked to be on track to bounce back from their midweek UEFA Champions League elimination by Manchester City, but were sensationally pegged back by Tuchel's former team as Bayern's winless streak stretched to four matches.
Sadio Mane gave Bayern a deserved first-half lead from close range, but Mainz showed signs of promise and built on such encouragement after the break when Ludovic Ajorque wiped out the lead.
Leandro Barreiro put Mainz in front 17 minutes from time and Aaron Martin's fine strike soon after finished Bayern off, gifting Borussia Dortmund the opportunity to go top later in the day.
Bayern threatened an early breakthrough when Mane coolly clipped over Mainz goalkeeper Robin Zentner in the 15th minute, only for his goal to be disallowed for offside.
But the visitors did take the lead just before the half-hour mark, Joao Cancelo's left-wing cross leaving Mane with the simplest of headed finishes at the back post.
The hosts were good value for their leveller after the hour, however.
Sommer could only parry Lee Jae-sung's effort and Ajorque was on hand to nod in from a few yards out.
That was merely the start for Mainz.
Eight minutes later, Karim Onisiwo fended off Josip Stanisic when meeting Ajorque's flick-on and subsequently teed up Barreiro, who confidently slotted home.
Martin then put the game beyond Bayern, smashing left-footed into the bottom-right corner from the edge of the box with 11 minutes remaining.
Borussia Dortmund's 4-0 thrashing of Eintracht Frankfurt later in the day put it back on top of the table by one point as this rollercoaster of a title tussle took another crazy twist.