After they both spent just one season in Germany's top flight, Duisburg were condemned to the second division after they lost 3-2 at home to champions Bayern, while Hansa Rostock's 2-1 defeat by Bayer Leverkusen sent them down.
Nuremberg - German Cup winners in 2007 - have one game left to save themselves following their 1-0 defeat at Hertha Berlin. Either Nuremberg or Arminia Bielefeld will be the third side to be relegated next weekend. Energie Cottbus made sure they stay in the Bundesliga with a shock 2-0 win at home to Hamburg.
Having been confirmed as Bundesliga champions last weekend, Bayern raced into a 3-0 lead only to concede two second half goals and had to cling on to their slender lead for a 3-2 win.
"We made life hard for ourselves by making too many errors and conceding the early goal," said Duisburg coach Rudi Bommer. "I appealed to the players' sense of honour at half-time as we were 3-0 down and we did well in the second half,” Bommer said. “But we are being relegated not based on today's performance, but based on what we have done over the last season."
Bayern have conceded 20 goals this season and are one game away from breaking Werder Bremen's record of 22 for the lowest number of goals leaked in a season.
Munich took an early lead at Duisburg when midfielder Andreas Ottl unleashed a right-footed shot from 21 metres after just three minutes.
"I couldn't believe we were 3-0 up after 20 minutes, I don't think anyone could," said Bayern coach Ottmar Hitzfeld. "Duisburg under-performed in the first half, but responded by pushing us hard and were on the verge of beating us by the final whistle,” he said. "Even though we have won the league, it is important we win our games, right up until the end of the season - we have a responsibility to our fans."
Germany striker Lukas Podolski netted twice in two minutes to put Bayern on to a 3-0 lead after just 20 minutes. But Duisburg fought back with two second half goals to put the champions under pressure at 3-2 with more than half an hour remaining.
Werder Bremen remain second in the league behind Bayern after their 6-1 hammering of Hanover 96.
Portuguese striker Hugo Almeida opened the scoring with a 14th minute goal, but the second half turned into a goal feast in Bremen before Hanover grabbed a consolation goal on the final whistle.
And third-placed Schalke - just two points behind - kept up the pressure on Bremen with a hard-fought 1-0 win at home to Eintracht Frankfurt.
Dark horses VfL Wolfsburg are on the verge of a UEFA Cup berth after their 4-0 humbling of VfB Stuttgart. The hosts took the lead when Brazilian Marcelinho netted after 16 minutes and things quickly went bad to worse when Stuttgart were reduced to 10 men after Fernando Meira was sent off after 18 minutes.
With four sides - Wolfsburg, Stuttgart, Bayer Leverkusen and Hamburg – all locked on 51 points and just two UEFA Cup places available, it will all be decided on the last day of the season next Saturday.