Bundesliga preview: 'Endurance test' as Dortmund face Wolfsburg
Dortmund, who lost the title to Bayern Munich on the final day of last season, have started this season poorly by their standards and were 2-0 losers at PSG in the Champions League in midweek.
They may still be unbeaten in the league but have laboured to two wins and two draws — all of which have come against teams in the bottom half of the table.
On Saturday, Edin Terzic's men take on Wolfsburg, who look refreshed under former Bayern coach Kovac, now in his second year in the Auto City.
Noted disciplinarian Kovac's well-drilled side have won three of four this season to sit one point ahead of Dortmund in the table.
One saving grace, however, for the home side on Saturday is their dominant recent record, not only head-to-head with Wolfsburg, but against Kovac-coached teams.
Wolfsburg have won just one of their past 16 games against Dortmund dating back to the 2015 German Cup final, which the Wolves won 3-1.
In that match, Kevin de Bruyne, in his final match for Wolfsburg, carved up Dortmund, who were also bidding farewell to coach Jurgen Klopp.
Wolfsburg have not won at Dortmund's Signal Iduna Park since 2012 and Kovac has lost all four games at the venue as coach of Wolfsburg, Bayern and Eintracht Frankfurt.
Speaking on Thursday, Kovac said simply "at some point these runs will come to an end".
Kovac called on his side to "be courageous" in the "endurance test", saying "when you act fearful in Dortmund it gets very difficult".
Bayern Munich, Bayer Leverkusen and RB Leipzig fill the top three places in the table with just one loss between them.
Harry Kane-powered Bayern may have met their match in last Friday's 2-2 draw with Xabi Alonso's impressive Leverkusen who lead the way on goal difference.
RB Leipzig have burst out of the blocks under former Dortmund mentor Marco Rose, scoring 19 and conceding just five in six competitive matches this season.
One to watch: Victor Boniface (Bayer Leverkusen)
Summer arrival Victor Boniface is one of the many top performers that have driven Bayer Leverkusen to the top of the table.
Boniface, 22, whose strong start won him a debut cap for Nigeria earlier in September, has four goals and two assists after just four league matches.
Leverkusen took a risk in signing Boniface, who had two serious knee injuries early in his career. With Xabi Alonso's side unbeaten atop the Bundesliga table — and Boniface in fine form — it looks like the risk is paying off.
Key stats
One in 17: Bochum have won just one of their past 17 matches against Bayern Munich dating back to 2004.
Eight in four: Stuttgart's Serhou Guirassy has eight goals in four league games this season - just three shy of the 11 he scored last season.
18 months: Champions League participants Union Berlin have lost their last two league matches in a row - the longest streak in a year and a half.
Fixtures (2.30pm BST unless stated)
Friday
Stuttgart v Darmstadt (7.30pm)
Saturday
Augsburg v Mainz, Bayern Munich v Bochum, Borussia Monchengladbach v RB Leipzig, Borussia Dortmund v Wolfsburg, Union Berlin v Hoffenheim, Werder Bremen v Cologne (5.30pm)
Sunday
Bayer Leverkusen v Heidenheim, Eintracht Frankfurt v Freiburg (4.30pm)
