Niko Kovac said his Borussia Dortmund players must dig deep to boost their confidence ahead of their Champions League play-off second leg against Sporting CP. 

Kovac watched on as Dortmund were beaten by lowly Bochum 2-0 in the Bundesliga on Saturday, leaving them languishing in 11th place in the German top-flight. 

But Kovac, who replaced Nuri Sahin as BVB's coach earlier this month, notched the first victory of his tenure in a 3-0 win over Sporting in the first leg of their play-off tie. 

Dortmund's win in the first leg was the 12th time they have won the first leg of a major European knockout stage tie away from home, progressing in each of the last 11.

They have also won four of their five meetings with Sporting in all competitions (L1), with both of their previous home games against them finishing 1-0.

Dortmund have only lost one of their last 15 home matches in the Champions League (W10 D4), with that lone defeat coming to Barcelona in December (2-3).

The German side have also netted 33 goals across these 15 matches, at an average of 2.2 per outing, but Kovac said past results are a distant memory for his side. 

"I am a football coach, and it is not the end of this play-off, just the first half," Kovac told a press conference on Tuesday, ahead of the second leg for a spot in the last 16.

"As coach you have to try to give the players that self-confidence.

"Through good training, good matches, through wins. As a coach, I see the results but also the good things that we do. We have to multiply those in matches," he added.

"These players are players of high quality, but at the moment the head is the key factor."

Dortmund's struggles in the Bundesliga this season have seen them drop eight points adrift of the final Champions League qualifying spot in the German top-flight. 

Indeed, many of their failures have come from their own doing, with Niklas Sule's weak backpass gifting Giorgos Masouras Bochum's second goal in their last Bundesliga defeat, which has been a story of their campaign so far. 

In the Bundesliga this season, only Bochum, RB Leipzig (both seven), Eintracht Frankfurt and Holstein Kiel (both eight) have made more errors leading to goals than Dortmund (five). 

"Three times in the past matches we allowed our opponents to run alone towards goal. We have to minimise those things," Kovac said.

"It is about relaxing the head, resetting it," he added. "What helps is training, success in training and most of all, wins.

"We are not stupid to say that this tie is done. We have to play as intensely as we can. We can't say we play only 50%, not in the Champions League."