Borussia Dortmund continued their impressive start to the season as Jude Bellingham scored in a comfortable 3-0 Champions League home win over FC Copenhagen on Tuesday.

With striker Sebastien Haller, who is currently undergoing treatment for testicular cancer, watching on in the stands, Dortmund were composed and dominant throughout despite fielding four Champions League debutants in the starting XI.

Dortmund captain Marco Reus said the crowd's jubilant reaction to Haller's presence in the stadium "gave him goosebumps".

Reus was proud of his side's effort against a team returning to the Champions League for the first time in six years, but knew they must improve to challenge Europe's heavyweights.

"First things first, I'm happy that we won this 'must-win' game," Reus told broadcaster Amazon Prime.

"But I know that we must improve against Manchester City next week, because there will be a different quality on the pitch.

"We didn't allow much. There would have been a bit more in it, but I don't want to be too critical. A win like this to start with feels good."

After a furious opening half dominated by the home side, Marco Reus dribbled past two Copenhagen defenders before hammering the ball past Australian goalkeeper Mathew Ryan on 35 minutes.

Just seven minutes later, American forward Giovanni Reyna -- who was subbed on for the injured Thorgan Hazard in the 23rd minute -- set Raphael Guerreiro up for an easy tap-in to double his side's lead.

Dortmund, who have won four from five in the Bundesliga this season, were roared on by their famous yellow wall, which was allowed to feature standing fans for the first time since 1998 under new UEFA regulations.

One minute into the second half, Copenhagen's Lukas Lerager had a chance to pull one back for his side but was denied by a superb reflex save by 'keeper Alex Meyer, making his Dortmund and Champions League debut.

"This was a day I will never forget," Meyer, who was plying his trade in the German second division last season, told German media after the game.

As the game wore on, Dortmund continued their dominance and went close several times through the creative Julian Brandt, before Bellingham converted another assist from Reyna in the 83rd minute.

Copenhagen looked to have scored a late consolation goal through Rasmus Falk, but it was chalked off for offside.

Dortmund coach Edin Terzic praised his side's composure and dominance.

"I think we did an excellent job," Terzic said. "That's a great start to our Champions League season."

The game was the fourth time in seven matches this term that Dortmund have kept a clean sheet.

Despite the win, Dortmund lost Hazard early and now have nine first-team players out injured just six weeks into the campaign.

Terzic lamented his side's bad injury luck after the game, telling reporters it was "brutally frustrating".

"It's not like we're not trying everything to change things - but we'll keep working on it."

Copenhagen continue their Champions League campaign next week at home to Sevilla, while Dortmund head away to take on former striker Erling Haaland's Man City.