Bayern Munich defeated Borussia Dortmund 4-2 in the debut match of their new coach Thomas Tuchel on Saturday to dethrone their rivals at the top of the Bundesliga table again with this title race statement win.
A howler from Dortmund goalkeeper Gregor Kobel gifted Bayern a 13th-minute lead which Thomas Müller increased to 3-0 with a brace over the next 10 minutes.
Kingsley Coman got a fourth shortly after the restart before Dortmund saved face from Emre Can's penalty in the 72nd and Donyell Malen late on.
Former Dortmund (and Paris Saint-Germain and Chelsea) coach Tuchel had during the international break taken over from Julian Nagelsmann who had to go after inconsistent Bundesliga performances since the January restart which had cost them the league.
Dortmund had turned a nine-point deficit into a one-point lead during that period with nine wins and a draw in their bid for a first trophy since 2012.
But they now had to swallow a ninth straight league defeat in Munich, with a goal difference of 8-37, as they slipped behind the 10-time reigning champions again.
"I was very nervous today. It was a good first step but there is still a lot of room for improvement," Tuchel told Sky TV. "The league lead will give us confidence.
"We knew what was at stake. A change of coach always leads to unrest. The team was 100% ready to suffer. When we played calmly we created top scoring opportunities. We were too nervous at first and a little sloppy after the break. We lost too many balls."
Dortmund captain Marco Reus said: "Gregor has won so many games for us. We had to digest it and then conceded again. We are all just human and it doesn't give you confidence. The result doesn't lie, we deserved the defeat. It was not a good night.
Looking at the title race, he added: "We have made up ground before. It will not be easy but we have to stay in pursuit. It is not over yet."
Dortmund had entered the game full of confidence from their long unbeaten run, and Reus was denied at the last instance by Bayern defender Matthijs de Ligt.
But it all unravelled for the visitors when in the 13th Kobel's attempted clearance of Dayot Upamecano's long ball went completely wrong against the charging Leroy Sane, and the ball trickled into the net.
Kobel, playing in a return from injury, said: "I won't blame a lack of matches. There are shit days, and today was one of them. It hurts a lot."
The goal shocked Dortmund, and Müller poked home off De Ligt's header for 2-0 in the 18th. Another five minutes later Kobel did not look good again on Sane's long-range drive, allowing Müller to capitalise on the rebound.
Dortmund had rallied from two goals back to 2-2 in the reverse fixture in autumn but there was no coming back this time as Coman made it 4-0 at the far left post five minutes after the restart off Sane.
Eric Maxim Choupo-Moting had an artistic fifth disallowed for offside before Dortmund got on the scoreboard from Can's spot kick, after Serge Gnabry had brought down Jude Bellingham, and Malen then also netted in the 90th.
Elsewhere, RB Leipzig's woes deepened with a third straight defeat in all competitions without scoring, 3-0 at home against in-form Mainz.
Freiburg were held 1-1 by Hertha Berlin, visiting Bayer Leverkusen ended Schalke's unbeaten run in the second half of the season with a 3-0 victory, and Wolfsburg drew 2-2 with Augsburg, and Union Berlin beat bottom club VfB Stuttgart 3-0.
Eintracht Frankfurt were held 1-1 by Bochum on Friday. Sunday's games are the Cologne v Mönchengladbach derby and Bremen v Hoffenheim.
