Jefferson Farfan scored the only goal for Schalke at Mainz in the Bundesliga on Sunday, with both teams missing a penalty.
The 1-0 win moves Schalke up to 10th with 19 points.
Mainz, which started the weekend in second place, drops to fourth with 30 points - 13 behind leader Borussia Dortmund.
Earlier, Papiss Demba Cisse took his Bundesliga season tally to 13 with two goals for Freiburg in a 3-0 victory over visiting Borussia Moenchengladbach.
Freiburg - with its fifth home win in six matches - climbs back up to fifth place with 26 points, one above defending champion Bayern Munich, while Moenchengladbach remains bottom.
Farfan scored in the 30th minute when Lukas Schmitz cut the ball back to Jose Manuel Jurado. The Spaniard's shot rebounded off teammate Raul Gonzalez and Farfan sent it in past goalkeeper Christian Wetklo.
Schalke missed a penalty in the eighth minute when Klaas-Jan Huntelaar crashed his effort off the left post. The rebound came off Wetklo's back for a corner.
The penalty decision was hotly contested as defender Christian Fuchs was judged to have brought Farfan down in the penalty area when contact appeared to have been made outside.
Goalkeeper Manuel Neuer - in his 60th straight game for Schalke - had to react quickly before half time to clear the ball from Andre Schuerrle when the 20-year-old was played through by a great pass from Elkin Soto.
In the second half the goalkeeper brought down substitute Adam Szalai in the area when the Hungarian was through on goal. Neuer escaped a booking despite being the last Schalke player, and he saved a very weak penalty effort from Schuerrle.
The rebound effort from Szalai was deflected onto the crossbar by Christoph Metzelder before the ball was eventually shepherded to safety.
Cisse opened the scoring for Freiburg against Borussia Moenchengladbach in the 19th minute when he got between two defenders to meet a perfect cross from Maximilian Nicu with a powerful header.
Freiburg almost gifted the visitors an equalizer when defender Heiko Butscher headed the ball back beyond the reach of Oliver Baumann. The goalkeeper beat Mohamadou Idrissou in a race to the ball before the striker could knock it into the empty net. Idrissou - a former Freiburg player - collided with the post and was later substituted at half time.
Moenchengladbach lost defender Roel Brouwers to injury at the end of the first half and Freiburg capitalized right away when Oliver Barth made it 2-0. Barth, a defender, was first to react when goalkeeper Christopher Heimeroth was unable to hold onto a powerful shot from Cisse.
The Senegalese completed the scoring in the 59th minute when he was left unmarked at the far post to meet a free kick from Julian Schuster with a simple tap in.
