With second-placed Bayern Munich being held to a goalless draw at home to Mainz on Saturday night, the Bavarians now have only a slender chance of denying Dortmund a second consecutive title.
"It feels good, but no, nothing has been decided yet," insisted Dortmund coach Jurgen Klopp, while president Reinhard Rauball said Borussia deserved to be where they are.
"In the last few days we have beaten the second and third placed teams in the table, so this team has earned their place at the top," he said after Borussia also beat Bayern 1-0 in Dortmund on Wednesday.
Bayern host Real Madrid in the Champions League semi-final, first-leg, on Tuesday and coach Jupp Heynckes paid the price for resting several stars as captain Philipp Lahm, wing Franck Ribery and striker Mario Gomez all started on the bench.
"This is obviously very disappointing for us, we had to score a goal," said Bayern's Germany star Bastian Schweinsteiger.
"Now we look towards Tuesday, because it's all or nothing. You can't just give 100 percent, you have to cross the line."
As Bayern were frustrated in Munich, Klopp's team took the opportunity to extend their lead but they had to come from behind in Gelsenkirchen.
"That was real work for all parties with Borussia Dortmund as the lucky winners," said Klopp, who has steadfastly refused to talk about the title.
"We squeezed out everything we had against a robust, physical opponent and we were better after it went 1-1. That was a hard opponent on a tough ground.
"After we took the lead, we defended with real passion, the team has a great character and never seems satisfied."
Schalke took the lead when Peru forward Jefferson Farfan blasted his shot home from the edge of the penalty area with just nine minutes on the clock, the ball deflecting off Dortmund's Shinji Kagawa.
But the champions roared back as Poland defender Lukasz Piszczek drilled home the equaliser from a seemingly impossible angle on 17 minutes.
Dortmund captain Sebastian Kehl then scored the winner on 63 minutes from a corner when Schalke defender Christoph Metzelder inadvertently headed down into Kehl's path and the visiting skipper fired home.
In claiming victory, Dortmund set a new Bundesliga record of 25 games without defeat.
They now face fourth-placed Borussia Moenchengladbach, bottom side Kaiserslautern and Freiburg before the league finishes on May 5, while Bayern face Werder Bremen, Stuttgart and Cologne in their title run-in.
Kaiserslautern have no more than a mathematical chance of avoiding relegation after they were beaten 2-0 at home by Nuremberg, which kept them nine points from safety.
Ten-man Hertha Berlin remain second from bottom despite picking up a point in a dramatic 3-3 draw at Bayer Leverkusen, after they scored three goals in 15 second-half minutes.
The hosts went 2-0 up in the second-half, but Berlin pulled a goal back when Germany Under-21 striker Pierre-Michel Lasogga scored with a header on 62 minutes.
Hertha were reduced to 10 men when captain Levan Kobiashvili brought down Swiss forward Eren Derdiyok in the area.
Hertha goalkeeper Thomas Kraft saved Simon Rolfes' penalty attempt on 66 minutes then five minutes later it was 2-2 as Turkey striker Tunay Torun equalised.
The 21-year-old grabbed his second on 77 minutes after Brazil striker Raffael counter-attacked and squared for his forward partner to drill home his shot, before Bayer's Stefan Kiessling equalised on 83 minutes.
Cologne, who are at Moenchengladbach on Sunday, are in the third relegation place, and now four points behind 15th-placed Augsburg, who poached a 2-1 win at Wolfsburg.
Hamburg also gave themselves a fighting chance of staying up with a 1-0 win at home to Hanover.
Stuttgart are fifth in the league and challenging for a Champions League place after their 4-1 hammering of Bremen on Friday night extended their run without defeat to nine games.
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