Hamburg's hopes of qualifying for a European place next season suffered a setback on Sunday when they lost 1-0 at mid-table Borussia Moenchengladbach.
The defeat at Gladbach leaves Bruno Labbadia's side sixth in the table and four points adrift of fifth-placed Werder Bremen with six games remaining and only the top five qualifying automatically for Europe.
"We were too naive," said Hamburg captain David Jarolim.
"We wanted to get into the top five, but now we have to pay attention we don't lose sixth place."
In a scrappy game, the winner came in the 43rd minute when Dutch defender Roel Brouwers poked the ball over the line after a goal-mouth scramble to give Gladbach only their third win in the last 10 games.
This was Hamburg's third defeat in their last five league matches and leaves them 14 points behind new league leaders Schalke.
Earlier, Freiburg drew 1-1 at Hoffenheim to remain in the drop zone.
The guests had looked on course to escape the bottom three with a second consecutive win after Cameroon striker Mohamadou Idrissou stabbed home on 64 minutes following a mix-up in the Hoffenheim defence.
But the hosts levelled when Croatian defender Josip Simunic netted in the 79th minute.
The result leaves Freiburg third from bottom and if they remain there until the season ends on May 8, they will face a play-off with the third-placed team in the second division for the right to stay in the top flight.
On Saturday, a Kevin Kuranyi double put Schalke top following a 2-0 win over Bayer Leverkusen, as Bayern Munich lost again in a sizeable setback ahead of Tuesday's Champions League clash against Manchester United.
Kuranyi scored both goals in the first half to put Felix Magath-coached Schalke two points clear at the top with six games remaining.
The Royal Blues, who are chasing their first German league title since 1958, also saw Kuranyi take over from Leverkusen's injured Stefan Kiessling as the league's joint top-scorer with 17 goals alongside Wolfsburg's Edin Dzeko.
The defeat left Leverkusen third in the table, five points behind the new leaders.
Bayern suffered a second consecutive league defeat when they slumped to a 2-1 home loss to Stuttgart.
The German giants must now pick themselves up in time to face Manchester United at the Allianz Arena on Tuesday in the Champions League quarter-final first leg and are waiting on the fitness of star forward Arjen Robben.
Greek striker Theofanis Gekas, who scored three goals against Wolfsburg, found the net with a second-half header, but the effort was ruled offside.
The result leaves Hertha four points from safety.
Werder Bremen remain on course for a top-five finish after a 4-2 win over relegation contenders Nuremberg despite finishing with 10 men.
Wolfsburg remain in mid-table after two late strikes from Dzeko secured a 2-0 win at Mainz.
Source: AFP Global Edition