Substitute Andreas Ivanschitz scored two minutes after coming off the bench to give Mainz a 1-0 victory at Bayer Leverkusen and return his team to the top of the Bundesliga on Sunday.
Mainz, which has won eight of nine games, opened a two-point lead over Borussia Dortmund, which drew 1-1 with Hoffenheim at home.
Substitute Antonio da Silva scored a contentious free kick two minutes into injury time to earn Borussia's point.
In the third match on Sunday, Stuttgart beat St. Pauli 2-0 to jump four places above the bottom.
Mainz survived some heavy pressure from Leverkusen in the first half and then produced a strong second half to stun Leverkusen.
Andre Schuerrle, who had come on together with Ivanschitz in the 68th minute, picked up a high ball after running behind Leverkusen's defense two minutes later and sent a perfect pass for Ivanschitz to slot home from close range.
Mainz, the surprise team of the season, now has 24 points and Dortmund 22. Mainz hosts Dortmund next week and could open a significant lead if it wins. Hannover is third, eight points behind Mainz.
In Dortmund, da Silva curled the free kick from the edge of the penalty area to cancel out a goal from Demba Ba after nine minutes. Dortmund missed a penalty in the first half and failed to set a club record by winning eight straight games.
"I kissed the ball before shooting, it was our last chance," da Silva said.
But coach Ralf Rangnick and Hoffenheim players protested loudly against the referee's decision to award the free kick.
"I went to the referee and I told him it was a foul on (Chinedu) Obasi and not by Obasi," Rangnick said.
With Hoffenheim players surrounding referee Wolfgang Stark after the final whistle, Sejad Salihovic was given a red card.
Hoffenheim outplayed Dortmund early in the match and took the lead when Demba Ba slotted home from close range off a good pass from Luiz Gustavo.
Dortmund had a chance to pull even in the 15th when Hoffenheim's defender Isaac Vorsah cleared the ball with his hand in front of Shinji Kagawa.
Nuri Sahin took the penalty and hit the target but had to repeat the shot as Lucas Barrios had stepped into Hoffenheim's area too quickly. Sahin took the second shot as well and this time chose to aim for Tim Starke's right side but the keeper read his shot and stopped the ball.
"It was ridiculous," Dortmund coach Juergen Klopp said of the referee's decision to repeat the penalty.
Starke made an outstanding save from Barrios in the 62nd, knocking away the point-blank shot with his knee.
Boris Vukcevic then had his shot punched away by Dortmund goalkeeper Roman Weidenfeller.
Dortmund had several free kicks late in the match and da Silva used the last one to salvage the draw.
"The way we rallied in the second half was incredible," Klopp said.
Hoffenheim coach Ralf Rangnick had to rush onto the field to try to calm down his players and keep them away from the referee after the end of the match.
Earlier, Cologne fired coach Zvonimir Soldo, one day after the club slipped to its sixth defeat of the season with a 2-1 a loss at Hannover and fell to the bottom of the standings.
