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Robert Lewandowski helped to see the league leaders to three hard-fought points shortly before the interval.

Second-placed Bayer Leverkusen will get the opportunity to close the gap which separates them from the summit when they entertainWolfsburg on Saturday.

Dortmund will be pleased to have put further daylight between themselves and the chasing pack after enduring a frustrating night againstCologne.

Visiting keeper Michael Rensing was in inspired form, repelling almost everything the hosts could throw at him.

He made a series of spectacular saves during the first half, helping to keep the game goalless.

Cologne's resistance was finally broken, though, a minute before the break when Lewandowski picked the ball up on the edge of the box and drilled home off the inside of the post.

Dortmund continued to press at the start of the second half and Rensing was forced to parry a stinging effort from Kevin Grosskreutz.

He was then called into action again moments later to deny Neven Subotic.

Remarkably, Cologne should have levelled on 56 minutes when Milivoje Novakovic raced clear, but he shot wide from eight yards out.

Dortmund hit the crossbar twice in the closing stages, through Lucas Barrios and Nuri Sahin, but they were forced to settle for a narrow one-goal success.