Marco Reus scored one goal and set up another as Borussia Moenchengladbach threw the Bundesliga title race wide open by beating leader Bayern Munich 3-1 Friday in the first game after the winter break.
Patrick Herrmann made it 2-0 in the 41st, and added another goal in the 71st after being set up by Reus.
Bastian Schweinsteiger, back after recovering from a broken collarbone, scored Bayern's 76th-minute consolation.
Moenchengladbach moves within one point of Bayern with the victory, while Schalke and defending champion Dortmund can both move level with Bayern on 37 points later this weekend.
''We played into 'Gladbach's hands with the early goal,'' said Bayern coach Jupp Heynckes, a former Moenchengladbach striker and coach.
Reus rejected Bayern's overtures this past offseason, instead opting for a ?17 million ($21.81 million) move to Dortmund, and the 22-year-old winger gratefully accepted Neuer's wayward clearance before dispatching it into the unguarded net for his 11th goal of the season.
Neuer's mistake in the opening fixture of the season also gave Moenchengladbach a 1-0 win in Munich last August.
As Bayern pushed for an equalizer, Herrmann struck at the end of a slick counterattack, when Mike Hanke split the defense with a crossfield pass.
''The second goal was crucial, just before the break,'' Heynckes said.
Herrmann sealed the win when he rounded Neuer to score from a tight angle, after Reus had waited for his support before playing the 21-year-old through with a perfect pass.
Schweinsteiger's reply five minutes later was not enough to prevent Moenchengladbach celebrating its first double over Bayern since the 1995-96 season.
''It was hard for Bayern to find a gap,'' Moenchengladbach coach Lucien Favre said. ''It was very important to take three points against Bayern again.''