In 2008, he moved with Klopp to become assistant manager at Borussia Dortmund. Described by Klopp as his "right hand", Buvač helped lead Dortmund to back-to-back Bundesliga wins in 2011 and 2012, as well as the DFB-Pokal in 2012, the DFL-Supercup in 2008, 2013 and 2014, and their second appearance in a Champions League final in 2013. In 2013, while still at Dortmund, Buvač also became the head coach of the Republika Srpska official football team.