Borussia Dortmund kept up the chase of Mainz at the top of the Bundesliga with their fifth straight victory at the expense of Bayern Munich.

Dortmund went ahead in the 52nd minute thanks to a goal from Lucas Barrios and Nuri Sahin sealed the win eight minutes later from a free-kick.

The result takes Dortmund ten points clear of Bayern and three behind leaders Mainz. Mario Gomez could have had a hat-trick for Bayern in the first 45 minutes but he failed to justify coach Louis van Gaal's decision to select him ahead of Miroslav Klose.

His first effort was a volley wide of the post in the seventh minute from Holger Badstuber's free-kick and then delayed too long when put through by Mark van Bommel, allowing Neven Subotic to slide in and clear.

Gomez was allowed the freedom of the area again in the 41st minute but this time his shot was deflected over the crossbar by Dortmund goalkeeper Roman Weidenfeller. And Gomez ended the first half by heading wide from a corner.

Martin Demichelis came on for his first appearance of the season as the replacement for the injured Daniel Van Buyten for the second half and he was to blame for Dortmund's goals.

His weak header provided Barrios with the chance to open the scoring seven minutes after the re-start, the Argentinian's shot taking a decisive deflection off Badstuber on its way past Hans-Jorg Butt.

Demichelis then gave away a free-kick for a handball on the edge of the penalty area, paving the way for Sahin to curl the ball into the top right-hand corner and double Dortmund's advantage.