Borussia Dortmund took advantage of Bayer Leverkusen's freefall by beating Nuremberg 3-0 at home to move to second in the Bundesliga on Saturday.
Leverkusen lost 1-0 at home to Mainz for its fifth consecutive defeat across all competitions, its eighth from 10 games. Eric Maxim Choupo-Moting scored with his heel in the 37th minute for Mainz, which was simply cleverer than the home side.
"There's a big concern that we'll miss all our targets," said Leverkusen sporting director Rudi Voeller, whose side faces an uphill challenge to overturn a 4-0 loss to Paris Saint-Germain in the Champions League and is already knocked out of the German Cup.
Second-half goals from Mats Hummels, Robert Lewandowski and Henrikh Mkhitaryan gave Dortmund a comfortable win after a difficult first half.
"We were often running around after them," Nuremberg striker Josip Drmic said. "They showed us how to do it and used their chances."
Werder Bremen beat Hamburger SV 1-0 in the league's 100th northern derby to leave its rival mired in the relegation playoff place.
Augsburg drew with Hannover 1-1 and Eintracht Braunschweig drew with Borussia Moenchengladbach by the same score.
Bayern Munich aimed to stretch its lead to 20 points with a win over Schalke late.
Nuremberg 'keeper Raphael Schaefer made a host of saves to ensure a frustrating first half for Dortmund, and Tomas Pekhart hit the post for the visitors.
The home side got off the mark in the 51st when Schaefer saved Lewandowski's header from Nuri Sahin's free kick, and Hummels followed-up on the line.
TV replays showed Lewandowski was marginally offside. The Poland striker hit his league-leading 15th goal in the 64th, when Mkhitaryan played him through to pick his spot.
Mkhitaryan rounded off the scoring with seven minutes remaining to round off a successful week for Dortmund, which beat Zenit St. Petersburg 4-2 in the Champions League on Tuesday, after losing 3-0 to Hamburg the weekend before.
"It was a tough piece of work," Dortmund coach Juergen Klopp said. "Nuremberg will certainly get enough points (to escape relegation)."
The same cannot be said of Hamburg. After beating Dortmund in new coach Mirko Slomka's first game in charge last week, the side slumped to its ninth defeat in 10 games.
Zlatko Junuzovic's 19th-minute strike was enough for Bremen to move six points clear. The Austrian midfielder was played through by Aaron Hunt's flick on with his heel.
Hakan Calhanoglu came closest for the visitors before the interval but Raphael Wolf got his fingertips to the ball as his shot crashed back off the crossbar.
"One goal chance in 90 minutes is too little," Hamburg defender Marcell Jansen said. "We'll fight against relegation to the last day."
The game was delayed for several minutes in the second half due to flares among the home fans.
Goalkeeping mistakes were responsible for both goals in Braunschweig. Moenchengladbach scored in the 25th when Braunschweig 'keeper Daniel Davari turned Raffael's corner into his own net.
The home side equalized in the 52nd when Marc-Andre ter Stegen — who is reportedly joining Barcelona at the end of the season — allowed Filip Daems' back pass slip behind and into the goal.