Klopp on the touchline seemed highly dissatisfied with the referee's decision and kept complaining to the fourth official.
However, the referee was the sole authority in a football match, so Dortmund's first attack of the game could only end in vain.
Although Dortmund had given the home side a warning right from the start, Napoli, a traditional Serie A powerhouse, were clearly not like the pushovers they had faced in the previous rounds of league matches.
Especially after the tactician Rafael Benitez took over this season, Napoli had improved greatly in defense.
The double defensive midfield pairing of Valon Behrami and Gokhan Inler could both organize attacks and defend fiercely.
Mkhitaryan received the ball several times in the middle and attacking third, only for Napoli to break up every attempt.
In the 10th minute of the match.
Having stabilized their midfield, Napoli finally began producing threatening attacks.
Insigne received a long pass from goalkeeper Pepe Reina on the left, then used consecutive changes of direction to shake off Kevin Grosskreutz.
"Great ball! Napoli are attacking!"
"Insigne... a diagonal pass into the box!"
"Higuain arrives... shoots directly at the near post!"
"Wonderful!"
"Weidenfeller reacted extremely quickly! He had already read Higuain's intentions and smothered the ball beneath him!"
"Although that was only Napoli's first shot, their efficiency was quite high."
"There was no hesitation at all in Insigne's pass just now. The moment he got past Grosskreutz, he delivered the ball immediately."
Klopp had not returned to the bench since the match began, remaining on the touchline as he watched the situation on the pitch.
After Higuain's shot was saved, he repeatedly gestured with both hands, signaling for the team to intensify their breakthroughs down the flanks.
Sahin passed the ball to Mkhitaryan, and the Armenian prepared to organize another attack.