Schalke failed to replicate their Champions League form from midweek, when they beat Hapoel Tel Aviv 3-1, and despite some good opportunities for Raul and Klaas-Jan Huntelaar were lucky to take a point after Halil Altintop missed a late chance for Frankfurt.
Schalke, last season's runners-up who spent millions of euros in the close season, are 15th in the league on six points after drawing three of their past four matches and losing the other.
"I can only smile because we are lucky to get away with a point," Schalke coach Felix Magath said. "We trembled for a long time. I cannot be satisfied with our game."
The hosts were taken by surprise early in the second half, with Germany international Aaron Hunt's deflected shot beating keeper Logan Bailly. Moenchengladbach cut the deficit via a Per Mertesacker own goal.
Peruvian Claudio Pizarro sealed Bremen's win in the 75th minute with his 134th Bundesliga goal, a record for a foreign player.
Cologne suffered a further setback in their bid to stay up, losing 2-1 at Hanover 96. Ivorian striker Didier Ya Konan scored twice to take his season's tally to five goals.
VfL Wolfsburg's lacklustre start under former England coach Steve McClaren continued when the 2009 champions slumped to 2-1 defeat to Nuremberg. Wolfsburg are 13th with 10 points.
"From the 46th minute onwards the game was under our control," Frankfurt coach Michael Skibbe said. "It is that domination that did not allow Schalke to develop their game. We were outstanding today."
