Bayer Leverkusen, led by coach Xabi Alonso, beat Bayern Munich 3-0 at home on Saturday to take a commanding five-point lead at the top of the Bundesliga table.
Munich-born defender Josip Stanisic, on loan from Bayern, scored the opener in the 18th minute and Alex Grimaldo added another early in the second half.
Jeremie Frimpong grabbed a third in injury time, scoring on the counter after Manuel Neuer came up for a Bayern corner, with Leverkusen rounding off an emphatic victory in style as they chase the club's first German title.
Bayern had few answers against an energetic and skillful Leverkusen side, fluent in attack, and kept tight control of star striker Harry Kane in defense.
With 13 games remaining this season, five-time runners-up Leverkusen now have a golden chance to break Bayern's 11-year reign in the Bundesliga and shed their unwanted "Neverkusen" moniker.
"From minute one until minute 90, we had our foot on the pedal," Leverkusen midfielder Robert Andrich told Sky.
Alonso told reporters "when you have players willing to make sacrifices, the team gets better."
A visibly frustrated Thomas Mueller lamented Bayern's dismal performance.
"Leverkusen were taking risks, looking for solutions and playing football," he said.
"We're playing from A to B, B to C – and nobody plays freely or takes risks."
Bayern came into the game under unusual pressure despite sitting just two points behind Leverkusen.
The game was delayed by 10 minutes due to ongoing protests against the German football association's decision to allow increased foreign investment, with fans throwing tennis balls and other objects onto the pitch as the players jogged to keep warm.
Despite the delay, Leverkusen showed none of the nerves seen among recent challengers for Bayern's crown, sticking to their high-risk, high-reward approach despite a tight press from the visitors.
Amine Adli had a half-chance and blasted straight at Neuer early, but it would be Stanisic who gave Leverkusen the lead against his parent club.
Stanisic beat new Bayern full-back Sacha Boey and tapped in a fine Andrich assist from close range, for the first Leverkusen goal.
Winners all 16 times they have taken the lead this season, the goal foreshadowed a period of Leverkusen dominance reminiscent of their best under Alonso, with Florian Wirtz and Jonathan Tah forcing last-ditch stops.
Not content to protect their lead, Leverkusen came out firing after the break and soon doubled their lead.
Summer signing Grimaldo collected Nathan Tella's pass and blasted past Neuer five minutes into the second half.
With the clock winding down, Neuer went up for a Bayern corner, allowing Leverkusen wing-back Frimpong to run the length of the field to seal a statement win.
Openda misses penalty
Elsewhere, RB Leipzig's hopes of closing in on the Champions League places suffered a blow, with striker Lois Openda missing a late penalty in a 2-2 draw at Augsburg.
Augsburg's Phillip Tietz gave the home side the lead late in the first half with a clean volley but Openda headed Leipzig level shortly after, his 15th goal of the season.
Slovenian striker Benjamin Sesko produced a carbon copy of Openda's header to put Leipzig ahead but Ermedin Demirovic pulled Augsburg back on level terms, blasting in with 30 minutes remaining.
Openda then had the chance to win it for Leipzig, but his spot-kick was kept out by Finn Dahmen, who has stopped four of the 12 Bundesliga penalties he has faced.
Leipzig, who were six points clear of Borussia Dortmund at the winter break, now sit three behind the fourth-placed club having won just one in five since Christmas.
Union Berlin won 1-0 at home to Wolfsburg in a match delayed by almost an hour due to protests against the German FA, Danilho Doekhi heading in the only goal in the 25th minute of first-half injury time.